Awhile ago we have created a set of xml schemas and xslt to represent different languages as xml, and to generate source from those xmls. This way we know to represent and generate: java, c#, cobol, and several sql dialects (read about languages xom on this site).

Here, we'd like to expose a nuisance we had with sql dialects schema.

Our goal was to define a basic sql schema, and dialect extensions. This way we assumed to express general and dialect specific constructs. So, lets consider an example.

General:

-- Select one row
select * from A

DB2:

select * from A fetch first row only

T-SQL:

select top 1 * from A

Oracle:

select * from A where rownum = 1

All these queries have common core syntax, while at the same time have dialect specific means to express intention to return first row only.

Down to the xml schema basic select statement looks like this:

<xs:complexType name="select-statement">
  <xs:complexContent>
    <xs:extension base="full-select-statement">
      <xs:sequence>
        <xs:element name="columns" type="columns-clause">
        <xs:element name="from" type="from-clause" minOccurs="0">
        <xs:element name="where" type="unary-expression" minOccurs="0"/>
        <xs:element name="group-by" type="expression-list" minOccurs="0"/>
        <xs:element name="having" type="unary-expression" minOccurs="0"/>
        <xs:element name="order-by" type="order-by-clause" minOccurs="0"/>
      </xs:sequence>
      <xs:attribute name="specification" type="query-specification"
        use="optional" default="all"/>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

Here all is relatively clear. The generic select looks like:

<sql:select>
  <sql:columns>
    <sql:column wildcard="true"/>
  </sql:columns>
  <sql:from>
    <sql:table name="A"/>
  </sql:from>
</sql:select>

But how would you define dialect specifics?

E.g. for T-SQL we would like to see a markup:

<sql:select>
  <tsql:top>
    <sql:number value="1"/>
  </tsql:top>
  <sql:columns>
    <sql:column wildcard="true"/>
  </sql:columns>
  <sql:from>
    <sql:table name="A"/>
  </sql:from>
</sql:select>

While for DB2 there should be:

<sql:select>
  <sql:columns>
    <sql:column wildcard="true"/>
  </sql:columns>
  <sql:from>
    <sql:table name="A"/>
  </sql:from>
  <db2:fetch-first rows="1"/>
</sql:select>

So, again the quesions are:

• how to define basic sql schema with goal to extend it in direction of DB2 or T-SQL?
• how to define an xslt sql serializer that will be also extendable?

Though we have tried several solutions to that problem, none is satisfactory enough. To allow extensions we have defined that all elements in sql schema are based on sql-element, which allows extensions:

<xs:complexType name="sql-element" abstract="true">
  <xs:sequence>
    <xs:element ref="extension" minOccurs="0" maxOccurs="unbounded"/>
  </xs:sequence>
</xs:complexType>

<xs:element name="extension" type="extension"/>

<xs:complexType name="extension" abstract="true">
  <xs:complexContent>
    <xs:extension base="sql-element"/>
  </xs:complexContent>
</xs:complexType>

...

<xs:element name="top" type="top-extension" substitutionGroup="sql:extension"/>

<xs:complexType name="top-extension">
  <xs:complexContent>
    <xs:extension base="sql:extension">
      <xs:sequence>
        <xs:element ref="sql:expression"/>
      </xs:sequence>
      <xs:attribute name="percent" type="xs:boolean" use="optional" default="false"/>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

Unfortunately, this creates too weak typed schema for extensions, thus intellisence suggests too many options.

On a way to a home we usually listen audio books in our car. In most cases these are science fiction stories. One of our favorite authors is Ray Bradbury. Probably you know his short story collection "The Martian Chronicles". Also, we like to glance over technology and science news to stay tuned in the latest innovations.

Recently, we've read an article that states that NASA is going to send a group of scientists-colonists to Mars in an observable future. It sounds in Ray Bradbury style.

Although, we're not specialists in this field, we discussed what difficulties may face such an expedition.

As far as we understand, there are following issues that must be solved before expedition may start:

• speed of a spaceship is yet too slow

• a shield from radiation doesn't exist

• big cargo section to contain sufficient reserve of water, food and oxygen for the expedition to survive

• a way to produce enough energy to survive on Mars

Actually, the second issue depends on the first one. At present there is no reliable long term protection from cosmic radiation, which can be installed on a spacecraft. At least we didn't hear about such thing. Thus, long staying in the open space will seriously harm colonists and may bring to naught the whole mission.

Сonsidering these facts, we concluded that a space travel further than the moon is not possible at present.

What could be done to solve these issues?

As a solution of space colonization could be the following. The earthlings won't send people but robots with corresponding equipment and containers for man, animals and plants DNAs or embryos. At the destination place robots will build a colony and will begin to grow people, animals, plants; to train them and to serve them later (at least to man " src="http://www.nesterovsky-bros.com/weblog/smilies/wink.gif"/> ).

How all this may solve the mentioned issues?

• It's much easier to create reliable shield from radiation for small DNA or embrios containers.

• time and speed of a spacecraft, in such case, will impact less on the mission.

• weight of spacecraft in this case could be less, or it may get more payload.

Thus, to bring the era of cosmic expansion, human kind must invest in the development of robotics, artificial intelligence, genetic engineering, development of rapid learning, among other scientific fields in space exploration.

Right now, you may see a beginning? of this trend in sciense here DFKI's robot ape to colonize the Moon?

In the far future, after the beginning will be forgotten, all this may lead to question: who was the first a man or a robot? " src="http://www.nesterovsky-bros.com/weblog/smilies/wink.gif"/>

While developing with KendoUI we have found kendo.ui.progress(container, toggle) function to be very useful. It's used to show or hide a progress indicator in the container element.

At the same time we have found that we usually used it in a context of async operation. This way, we want to show progress, perform some asynchronous operations, hide progress. So, we clearly want to benifit from RAII pattern: we would like to open a progress scope, and to perform some activity withing this scope.

Arguing like this, we have defined a utility function, which is the fusion of kendo.ui.progress() and $.when(). Its signature is like this:

nesterovskyBros.progress = function(instance /*, task ... */)

where instance is either Model, Widget, JQuery or DOM Element, and task is one or more deferred objects. This function shows a progress and returns a Promise that will hide a progress when all tasks will be complete. Implementation is trivial, so we quote it here:

// Fusion of kendo.ui.progress() and $.when().
scope.progress = function(instance /*, task ... */)
{
  if (instance instanceof Model)
  {
    instance = instance.owner && instance.owner();
  }

  if (instance instanceof Widget)
  {
    instance = instance.element;
  }

  if (instance && instance.nodeType)
  {
    instance = $(instance);
  }

  var id = ns + "-progress"; // "nesterovskyBros-progress";
  var progress = (instance && instance.data(id)) || 0;

  if (arguments.length < 2)
  {
    return progress;
  }

  var result = $.when.apply(null, [].slice.call(arguments, 1));

  if (instance)
  {
    instance.data(id, ++progress);
    kendo.ui.progress(instance, progress > 0);

    result.always(
      function()
      {
        progress = instance.data(id) || 0;
        instance.data(id, --progress);
        kendo.ui.progress(instance, progress > 0);
      });
  }

  return result;
};

The use is like this:

nesterovskyBros.progress(element, $.ajax("/service1"), $.ajax("/service2")).then(myFunc);

The code can be found at controls.js.

While trying to generalize our practices from KendoUI related projects we've participated so far, we updated control.js - a small javascript additions to KendoUI.

At present we have defined:

1. An extended model. See KendoUI extended model.

2. A lightweight user control - a widget to bind a template and a model, and to facilitate declarative instantiation. See KendoUI User control.

3. A reworked version of nesterovskyBros.defineControl() function.

var widgetType = scope.defineControl(
{
   name: widget-name-string,
   model: widget-model-type,
   template: optional-content-template,
   windowOptions: optional-window-options
},
base);

When optional-content-template is not specified then template is calculated as following:

var template = options.temlate || proto.template || model.temlate;

if (template === undefined)
{
  template = scope.template(options.name.toLowerCase() + "-template");
}

When windowOptions is specified then widgetType.dialog(options) function is defined. It's used to open dialog based on the specified user control. windowOptions is passed to kendo.ui.Window constructor. windowOptions.closeOnEscape indicates whether to close opened dialog on escape.

widgetType.dialog() returns a kendo.ui.Window instance with content based on the user control. Window instance contains functions:

• result() - a $.Deffered for the dialog result, and
• model() - referring to the user control model.

 The model instance has functions:

•  dialog() referring to the dialog, and
• result() referring to the dialog result.

widget.dialog() allows all css units in windowOptions.width and windowOptions.height parameters.

base - is optional user control base. It defaults to nesterovskyBros.ui.UserControl.

4. Adjusted splitter. See Adjust KendoUI Splitter.

5. Auto resize support.

Layout is often depends on available area. One example is Splitter widget that recalculates its panes when window or container Splitter is resized. There are other cases when you would like to adjust layout when a container's area is changed like: adjust grid, tab, editor or user's control contents.

KendoUI does not provide a solution for this problem, so we have defined our own.

• A widget can be marked with class="auto-resize" marker;
• A widget may define a widgetType.autoResize(element) function that adapts widget to a new size.
• A code can call nesterovskyBros.resize(element) function at trigger resizing of the subtree.

To support existing controls we have defined autoResize() function for Grid, Splitter, TabStrip, and Editor widgets.

To see how auto resizing works, it's best to look into index.html, products.tmpl.html, and into the implementation controls.js.

Please note that we consider controls.js as an addition to KendoUI library. If in the future the library will integrate or implement similar features we will be happy to start using their API.

See also: Compile KendoUI templates.

We heavily use kendo.ui.Splitter widget. Unfortunately it has several drawbacks:

• you cannot easily configure panes declaratively;
• you cannot define a pane that takes space according to its content.

Although we don't like to patch widgets, in this case we found no better way but to patch two functions: kendo.ui.Splitter.fn._initPanes, and  kendo.ui.Splitter.fn._resize.

After the fix, splitter markup may look like the following:

<div style="height: 100%" data-role="splitter" data-orientation="vertical">
  <div data-pane='{ size: "auto", resizable: false, scrollable: false }'>
    Header with size depending on content.
  </div>
  <div data-pane='{ resizable: false, scrollable: true }'>
    Body with size equal to a remaining area.
  </div>
  <div data-pane='{ size: "auto", resizable: false, scrollable: false }'>
    Footer with size depending on content.
  </div>
</div>

Each pane may define a data-pane attribute with pane parameters. A pane may specify size = "auto" to take space according to its content.

The code can be found at splitter.js A test can be seen at splitter.html.

Although WCF REST service + JSON is outdated comparing to Web API, there are yet a lot of such solutions (and probably will appear new ones) that use such "old" technology.

One of the crucial points of any web application is an error handler that allows gracefully resolve server-side exceptions and routes them as JSON objects to the client for further processing. There are dozen approachesin Internet that solve this issue  (e.g. http://blog.manglar.com/how-to-provide-custom-json-exceptions-from-as-wcf-service/), but there is no one that demonstrates error handling ot the client-side. We realize that it's impossible to write something general that suits for every web application, but we'd like to show a client-side error handler that utilizes JSON and KendoUI.

On our opinion, the successfull error handler must display an understandable error message on one hand, and on the other hand it has to provide technical info for developers in order to investigate the exception reason (and to fix it, if need):

You may download demo project here. It contains three crucial parts:

• A server-side error handler that catches all exceptions and serializes them as JSON objects (see /Code/JsonErrorHandler.cs and /Code/JsonWebHttpBehaviour.cs).
• An error dialog that's based on user-control defined in previous articles (see /scripts/controls/error.js, /scripts/controls/error.resources.js and /scripts/templates/error.tmpl.html).
• A client-side error handler that displays errors in user-friendly's manner (see /scripts/api/api.js, method defaultErrorHandler()).

Of course this is only a draft solution, but it defines a direction for further customizations in your web applications.

Useful links to those who are still dealing with Cool:GEN.

• Information Engineering Technology
• IET Gen Development Blog

The site is not cool by itself, but the value is in the tools that authors provide to simplify Cool:GEN development. Especially we would like to mention:

• GuardIEn - Version control, change and model management and automated builds for CA Gen, and
• VerifIEr - Automated code checking and standards verification.

These tools help to manage clean and error free models, which simplifies next migration to Java and C# that we perform.

We have upgraded KendoUI and have found that kendo window has stopped to size properly.

In the old implementation window set dimensions like this:

_dimensions: function() {
  ...
  if (options.width) {
    wrapper.width(options.width);
  }
  if (options.height) {
    wrapper.height(options.height);
  }
  ...
}

And here is a new implementation:

_dimensions: function() {
  ...
  if (options.width) {
    wrapper.width(constrain(parseInt(options.width, 10), options.minWidth, options.maxWidth));
  }
  if (options.height) {
    wrapper.height(constrain(parseInt(options.height, 10), options.minHeight, options.maxHeight));
  }
  ...
}

Thus nothing but pixels are supported. Earlier we often used 'em' units to define dialog sizes. There was no reason to restrict it like this. That's very unfortunate.

To simplify KendoUI development we have defined nesterovskyBros.data.Model, which extends kend.data.Model class.

Extensions in nesterovskyBros.data.Model

1. As with kendo.data.Model there is fields Object - a set of key/value pairs to configure the model fields, but fields have some more options:
   • fields.fieldName.serializable Boolean - indicates whether the field appears in an object returned in model.toJSON(). Default is true.
   • fields.fieldName.updateDirty Boolean - indicates whether the change of the property should trigger dirty field change. Default is true.
2. When model defines a field and there is a prototype function with the same name then this function is used to get and set a field value.
3. When property is changed through the model.set() method then dirty change event is triggered (provided that fields.fieldName.updateDirty !== false). This helps to build a dependcy graph on that property.
4. When model instance is consturcted, the data passed in are validated, nullable and default values are set.

Model example

Here is an example of a model:

nesterovskyBros.data.ProductModel = nesterovskyBros.data.Model.define(
{

fields:
{
  name: { type: "string", defaultValue: "Product Name" },
  price: { type: "number", defaultValue: 10 },
  unitsInStockValue: { type: "number", defaultValue: 10, serializable: false },
  unitsInStock: { type: "string" }
},

unitsInStock: function(value)
{
  if (value === undefined)
  {
    var count = this.get("unitsInStockValue");

    return ["one", "two", "three", "four"][count] || (count + "");
  }
  else
  {
    this.set("unitsInStockValue", ({one: 1, two: 2, three: 3, four: 4 })[value] || value);
  }
}

});

Notice that:

• unitsInStock property is implemented as a function - this helps to map model values to presentation values.
• when you call model.toJSON(), or JSON.stringify() you will see in result name, price, unitsInStock values only - this helps to get model's state and to store it somewhere (e.g. in sessionStorage).
• in a code:
    var model = new nesterovskyBros.data.ProductModel({ price: "7", unitsInStock: "one" });
  the following is true:
    (typeof(model.price) == "number") && (mode.price == 7) && (model.name == "Product Name") && (model.unitsInStockValue == 1)

As with UserControl the implemntation is defined in the controls.js. The sample page is the same index.html

Two weeks ago we've gotten new Lenovo 13" laptops (Yoga-13 with touch screens and Windows 8 Pro on board).

The first expression was WOW! Touch screens! Windows 8! Now we'll try our hand on that new (for us) API. So new, so cool...

A day later. What a shit this new UI. Where are my desktop, "Start" button, all the programs... After googling we've understood - we're not alone.

Few more days later. We've recognized that our SSD hard disk won't live long life with our projects. We generates output several GB a day. Thus we've decided to buy external SD cards - additional 64Gb, class 10. That's enough for us. No sooner said than done. After several attempts to copy our projects from hard drive to SD card (~9Gb of sources) we strongly believe that such a vigorous mix (Lenovo + Win 8 + external SD card) won't survive. Windows 8 hangs up when display off (in middle of data copy, after an hour of work). What a .... of .... this Windows 8, Lenovo and SD cards all together.

Developing with KendoUI we try to formalize tasks. With this in mind we would like to have user controls.

We define user control as following:

It is a javascript class that extends Widget.
It offers a way to reuse UI.
It allows to define a model and a template with UI and data binding.

Unfortunately, KendoUI does not have such API, though one can easily define it; so we have defined our version.

Here we review our solution. We have taken a grid KendoUI example and converted it into a user control.

User control on the page

See index.html

<!DOCTYPE html>
<html>
<head>
  <title>Test</title>

  <!-- (1) Include templates for controls. -->
  <script src="scripts/templates.js"></script>

  <script src="scripts/jquery/jquery.js"></script>
  <script src="scripts/kendo/kendo.web.min.js"></script>

  <!-- (2) UserControl definition. -->
  <script src="scripts/controls.js"></script>

  <!-- (3) Confirm dialog user control. -->
  <script src="scripts/controls/confirm.js"></script>

  <!-- (4) Products user control. -->
  <script src="scripts/controls/products.js"></script>

  <link href="styles/kendo.common.min.css" rel="stylesheet" />
  <link href="styles/kendo.default.min.css" rel="stylesheet" />
  <script>
$(function ()
{
  // (5) Bind the page.
  kendo.bind(
    document.body,
    // (6) Model as a datasource.
    { source: [new nesterovskyBros.data.ProductsModel] });
});
  </script>
</head>
<body>
  <!-- (7) User control and its binding. -->
  <div data-role="products" data-bind="source: source"></div>
</body>
</html>

That's what we see here:

1. Templates that define layouts. See "How To: Load KendoUI Templates from External Files", and templates.tt.
2. Definition of the UserControl widget.
3. Confirm dialog user control (we shall mention it later).
4. Products user control.
5. Data binding that instantiates page controls.
6. Model is passed to a user control through the dataSource.
7. Use of Products user control. Notice that "data-role" defines control type, "source" refers to the model.

User Control declaration

Declaration consists of a view and a model.

View is html with data binding. See products.tmpl.html

We build our project using Visual Studio, so templates packaging is done with templates.tt. This transformation converts products template into a tag:

<script id="products-template" type="text/x-kendo-template">

thus template can be referred by a utility function: nesterovskyBros.template("products-template").

Model inherits kedo.data.Model. Here how it looks:

// (1) Define a ProducsModel class.
nesterovskyBros.data.ProductsModel = kendo.data.Model.define(
{

// (2) Model properties.
fields:
{
  productName: { type: "string", defaultValue: "Product Name" },
  productPrice: { type: "number", defaultValue: 10 },
  productUnitsInStock: { type: "number", defaultValue: 10 },
  products: { type: "default", defaultValue: [] }
},

// (3) Model methods.
addProduct: function () { ... },
deleteProduct: function (e) { ... },
...

});

// (4) Register user control.
nesterovskyBros.ui.Products = nesterovskyBros.defineControl(
{
  name: "Products",
  model: nesterovskyBros.data.ProductsModel
});

That's what we have here:

1. We define a model that inherits KendoUI Model.
2. We define model fields.
3. We define model methods.
4. Register user control with  nesterovskyBros.defineControl(proto) call, where:
   
   • proto.name - defines user control name;
   • proto.model - defines model type;
   • proto.template - defines optional template. If not specified, a template is retrieved from $("#" + proto.name.toLowerCase() + "-template").html().

UserControl API

Now, what's remained is API for the UserControl. See controls.js.

1. UserControl defines following events:
   
   • change - triggered when data source is changed;
   • dataBound - triggered when widget is data bound;
   • dataBinding - triggered befor widget data binding;
   • save - used to notify user to save model state.
2. UserControl defines following options:
   
   • autoBind (default false) - autoBind data source;
   • template (default $.noop) - user control template.
3. UserControl defines dataSource field and setDataSource() method.
4. UserControl defines rebind() method to manually rebuild widget's view from the template and model.
5. UserControl sets/deletes model.owner, which is a function returning a user control widget when model is bound/unbound to the widget.
6. When UserControl binds/unbinds model a model.refresh method is called, if any.
7. You usually define you control with a call nesterovskyBros.defineControl(proto). See above.
8. There is also a convenience method to build a dialog based on a user control: nesterovskyBros.defineDialog(options), where
   
   • options.name - a user control name (used in the data-role);
   • options.model - a model type;
   • options.windowOptions - a window options.
   This method returns a function that recieves a user control model, and returns a dialog (kendo.ui.Window) based on the user control.
   Dialog has model() function that returns an instance of model.
   Model has dialog() function that returns an instance of the dialog.
   Dialog and model have result() function that returns an instance of deferred object used to track dialog completion.
   The example of user control dialog is confirm.js and confirm.tmpl.html. The use is in the products.js deleteProduct():
   

   deleteProduct: function(e)
{
  var that = this;

  return nesterovskyBros.dialog.confirm(
  {
    title: "Please confirm",
    message: "Do you want to delete the record?",
    confirm: "Yes",
    cancel: "No"
  }).
  open().
  center().
  result().
  then(
    function(confirmed)
    {
      if (!confirmed)
      {
        return;
      }
      ...
   });
}

Last

User controls along with technique to manage and cache templates allow us to build robust web applications. As the added value it's became a trivial task to build SPA.

See also: Compile KendoUI templates.

At present we inhabit in jquery and kendoui world.

There you deal with MVVM design pattern and build you page from blocks. To avoid conflicts you usually restrict yourself from assigning ids to elements, as they make code reuse somewhat problematic.

But what if you have a label that you would like to associate with an input. In plain html you would write:

<label for="my-input">My label:</label> <input id="my-input" type="text">

Html spec suggests to use element id to build such an association.

So, how to avoid introduction of id, and to allow to select input while clicking on the label?

In our projects we use a little utility function that solves exactly this task. It's easier to quote an example than to describe implementation:

<!DOCTYPE html>
<html>
<head>
  <title>Label</title>
  <script src="scripts/jquery.js"></script>
</head>
<body>
<div class="view">
  <div>A template:</div>
  <table>
    <tr>
      <td><label data-for="[name=field1]">Name1:</label></td>
      <td><input name="field1" type="text" /></td>
    </tr>
    <tr>
      <td><label data-for="[name=field2]">Name2:</label></td>
      <td><input name="field2" type="text" /></td>
    </tr>
    <tr>
      <td><label data-for="[name=field3]">Name3:</label></td>
      <td><input name="field3" type="text" /></td>
    </tr>
    <tr>
      <td><label data-for="[name=field4]">Name4:</label></td>
      <td><input name="field4" type="checkbox" /></td>
    </tr>
    <tr>
      <td><label data-for="[name=field5][value=0]">Name5:</label></td>
      <td><input name="field5" value="0" type="radio" /></td>
    </tr>
    <tr>
      <td><label data-for="[name=field5][value=1]">Name6:</label></td>
      <td><input name="field5" value="1" type="radio" /></td>
    </tr>
  </table>
</div>
<script>
$(document).on(
  "click",
  "label[data-for]",
  function(e)
  {
    var target = $(e.target);

    target.closest(target.attr("data-view") || ".view").
      find(target.attr("data-for")).
      filter(":visible:enabled").first().click().focus().
      filter("input[type=checkbox],input[type=radio]").change();
  });
</script>
</body>
</html>

In our applications we must support IE 8, and unfortunately we hit some leak, which is registered as Ticket #7054(closed bug: fixed).

While bug declared closed as fixed we can see that memory leak in IE8 like a mad. Not sure if something can be done about it.

The test case is:

<!DOCTYPE html>
<html>
<head>
  <title>Test</title>
  <script src="scripts/jquery/jquery-1.9.0.js"></script>
</head>
<body>
<script>
function testLeak()
{
  var handler = function () { };

  $('<div></div>').html(new Array(1000).join(new Array(1000).join('x'))).bind('abc', handler).appendTo('#test').remove();
}

$(function() { setInterval(testLeak, 1000); });
</script>
<div id="test"></div>
</body>
</html>

Update: jaubourg has pointed that we have missed to define element with id="test". With this element leak stops.

Kendo UI Docs contains an article "How To: Load Templates from External Files", where authors review two way of dealing with Kendo UI templates.

While using Kendo UI we have found our own answer to: where will the Kendo UI templates be defined and maintained?

In our .NET project we have decided to keep templates separately, and to store them under the "templates" folder. Those templates are in fact include html, head, and stylesheet links. This is to help us to present those tempates in the design view.

In our scripts folder, we have defined a small text transformation template: "templates.tt", which produces "templates.js" file. This template takes body contents of each "*.tmpl.html" file from "templates" folder and builds string of the form:

document.write('<script id="footer-template" type="text/x-kendo-template">...</script><script id="row-template" type="text/x-kendo-template">...</script>');

In our page that uses templates, we include "templates.js":

<!DOCTYPE html>
<html>
  <head>
    <script src="scripts/templates.js"></script>
    ...

Thus, we have:

• clean separation of templates and page content;
• automatically generated templates include file.

WebTemplates.zip contains a web project demonstrating our technique. "templates.tt" is text template transformation used in the project.

See also: Compile KendoUI templates.

Our goal is to generate reports in streaming mode.

At some point we need to deal with data streams (e.g. xml streams for xslt transformations). Often a nature of report demands several passes through the data. To increase performance we have defined a class named StreamResource. This class encapsulates input data, reads it once and caches it into a temp file; thus data can be traversed many times. StreamResource can read data lazily or in a eager way thus releasing resources early. This class can be used as a variation of PipeStream, which never blocks, as if a size of a buffer is not limited, and which can be read many times.

The API looks like this:

public class StreamResource: IDisposable
{
  /// <summary>
  /// Creates a StreamSource instance.
  /// </summary>
  /// <param name="source">
  /// A function that returns source as an input stream.
  /// </param>
  /// <param name="settings">Optional settings.</param>
  public StreamResource(Func<Stream> source, Settings settings = null);

  /// <summary>
  /// Creates a StreamSource instance.
  /// </summary>
  /// <param name="source">
  /// A function that writes source data into an output stream.
  /// </param>
  /// <param name="settings">Optional settings.</param>
  public StreamResource(Action<Stream> source, Settings settings = null);

  /// <summary>
  /// Gets an input stream.
  /// </summary>
  /// <param name="shared">
  /// Indicates that this StreamResouce should be disposed when returned
  /// stream is closed and there are no more currently opened cache streams.
  /// </param>
  /// <returns>A input stream.</returns>
  public Stream GetStream(bool shared = false);
}

The use pattern is following:

// Acquire resource.
using(var resource = new StreamResource(() => CallService(params...)))
{
  // Read stream.
  using(var stream = resource.GetStream())
  {
    ...
  }

  ...

  // Read stream again.
  using(var stream = resource.GetStream())
  {
    ...
  }
}

StreamResource is efficient even if you need to process content only once, as it monitors timings of reading of source data and compares it with timings of data consumption. If the difference exceeds some threshold then StreamResource caches source greedily, otherwise source is pooled lazily. Thus, input resources can be released promptly. This is important, for example, when the source depends on a database connection.

The use pattern is following:

// Acquire resource and get shared stream.
using(var stream = new StreamResource(() => CallService(params...)).GetStream(true))
{
  ...
}

Finally, StreamResource allows to process data in a pipe stream mode. This is when you have a generator function Action<Stream> that can write to a stream, and you want to read that data. The advantage of StreamResource over real pipe stream is that it can work without blocking of generator, thus releasing resources early.

The use pattern is similar to the previous one:

using(var stream = new StreamResource(output => Generate(output, params...)).GetStream(true))
{
  ...
}

The source of the class can be found at Streaming.zip.