Blog: Posts from October, 2008

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Posts from October, 2008
Friday, October 31, 2008PrintSubscribe
Upload and Download of BLOB in AJAX Applications

Data Aquarium Framework introduces a new feature that allows code-free uploading and downloading of Binary Large Objects to/from a database table column in AJAX style. The feature is based on a generic handler blob.ashx from File Upload premium project.

Here is screen shot from a sample application available at


If a BLOB field is storing an image then a thumbnail preview is automatically created. A preview is available in all views. Other types of BLOB are presented by a simple download hyperlink. Views are displaying additional controls that allow BLOB uploading when records are presented in edit or detail mode.


BLOB support is enabled only when you are interacting with existing records. BLOB data cannot be uploaded when creating new records. The internal preview and upload mechanism is based on automatic table row references based on primary keys, which makes uploading of BLOB impossible when records are created.

Original BLOB data can be retrieved from a database with a click of mouse. Here is a screen shot from Adventure Works application that shows side-by-side small and large photographs of products. Original BLOB data other then images will be opened by native applications when downloaded completely by your web browser.


A confirmation message is displayed at the top of the page when a BLOB data has been uploaded successfully.


You can find complete implementation details for all of these features in the project source code.

Making It Work

Generate a Data Aquarium Framework application from Northwind database and open ~/Contollers/Categories.xml data controller descriptor. Find definition of Picture field. It must look like the one below.

<field name="Picture" type="Byte[]" onDemand="true" 
  onDemandHandler="CategoriesPicture" onDemandStyle="Thumbnail" 
  allowQBE="false" allowSorting="false" label="Picture" />

Three attributes are turning on the BLOB support. Attribute sourceFields must list all fields that allow to find the row with a BLOB. This information is passed on to a generic handler blob.ashx located in the root of your web site project. The name of the handler is specified by onDemandHandler attribute. Optional style for an on-demand field is controlled by onDemandStyle attribute.

Generic handler blob.ashx is automatically generated by Code OnTime Generator. All handlers discovered in your database are listed at the top of the file.

Here is how they look in a Northwind application written in C#.

public partial class BlobFactory
    static BlobFactory()
        // register blob handlers
        RegisterHandler("CategoriesPicture", "\"dbo\".\"Categories\"", "\"Picture\"", 
            new string[] {"\"CategoryID\""}, "Categories Picture", String.Empty);
        RegisterHandler("EmployeesPhoto", "\"dbo\".\"Employees\"", "\"Photo\"", 
            new string[] {"\"EmployeeID\""}, "Employees Photo", String.Empty);

You can quickly change these handlers and add the new ones when needed. The parameters of RegisterHandler method are easy to understand.


The first parameter defines a key that is provided as a value for onDemandHandler attribute in data controller descriptors. The second parameter is a fully qualified name of the table that stores BLOB values. The third parameter specifies a column name of a BLOB. A list of key columns of this table follows in the fourth parameter. A user-friendly name of the blob in the fifth parameter is for GUI presentation.

The last parameter defines a content type of a BLOB. If the value is an empty string then the code of generic handler will try to automatically find the content type by treating the value as an image. If you are storing a specific type of data other then image then enter a valid content type that matches the BLOB. For example, if you are storing Microsoft Word documents then use application/msword as content type.

Friday, October 31, 2008PrintSubscribe
Export to Spreadsheet

Data Aquarium Framework applications are now supporting automatic exporting in Comma-Separated Values format.

Apply filters and sort your grid views the way you like. Select Actions on action bar and choose Export to Spreadsheet option.


A data file will be created on the server and a new web browser window will be launched to download the result. Your spreadsheet processor will automatically launch and displayed data.


The sort order, custom filters, and data formatting will be displayed similar to what you see in a grid view.

This feature is automatically available to all premium project subscribers.

Sunday, October 12, 2008PrintSubscribe
Using Oracle Sequence

Oracle database server provides support for sequences of unique values that are typically used to generate unique IDs for primary key columns or new records. Data Aquarium Framework and Aquarium Express are supporting automatic execution of static SQL statements just before a table record insertion takes place.

Consider the application created from HR demo schema that comes with Oracle database servers. The DEPARTMENTS table has a matching DEPARTMENTS_SEQ sequence that can be used to supply unique values for the primary key DEPARTMENT_ID.

Form createForm1 is displayed below. You can see that the primary key field is visible on the form and can be changed by user.


Let's modify the data controller descriptor ~/Controllers/HR_DEPARMENTS.xml to use the sequence for primary key column values.

The first step is a definition of command that executes just before a new record is inserted into database.

<command id="GetSequence" type="Text" event="Inserting">
  <text><![CDATA[select departments_seq.nextval from dual]]></text>
    <fieldOutput fieldName="DEPARTMENT_ID"/>

Attribute event tells the framework about the timing of execution, element text defines the actual SQL statement, and element fieldOutput directs the framework to copy the first column in the first row of command result set to the DEPARTMENT_ID field.

The second and last step of modification is to hide the DEPARMENT_ID field from user interface.

<view id="createForm1" type="Form" commandId="command1" 
  label="New Hr Departments">
  <headerText>Please fill this form and click OK button to create 
    a new hr departments record. Click Cancel to return to the 
    previous screen.</headerText>
    <category headerText="New Hr Departments">
      <description>Complete the form. Make sure to enter all 
        required fields.</description>
        <dataField fieldName="DEPARTMENT_ID" columns="15" hidden="true"/>
        <dataField fieldName="DEPARTMENT_NAME" columns="30" />
        <dataField fieldName="MANAGER_ID" aliasFieldName="MANAGER_LAST_NAME" />
        <dataField fieldName="LOCATION_ID" aliasFieldName="LOCATION_CITY" />

Attribute hidden on the field DEPARMENT_ID does the job.

Here is how the form is changed.


The new department is displayed in the list below.