Upload and Download / Blob Adapters

  File System

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Upload and Download / Blob AdaptersPrint||
File System

A local or remote file system is the most common method to store large binary content. Let’s implement a customer photo field in the Northwind database. Several utility fields in the Customers table will store file name, size, and type. The file itself will be stored in a specified folder location.

Adding Utility Fields to the Database

Start SQL Server Management Studio. In the Object Explorer, right-click on Databases / Northwind / dbo.Customers and press Design.

Designing the Customers table of Northwind database.

Add the following columns:

Column Name Data Type Allow Nulls
PhotoFileName nvarchar(250) yes
PhotoLength int yes
PhotoContentType nvarchar(50) yes

Save the changes to the table.

Start the web application generator. Click on the project name, and press Refresh. Check the box next to Customers controller and proceed to refresh the web app.

Refreshing the Customers table.

Configuring BLOB Field

Start the Project Designer. In the Project Explorer, switch to the Controllers tab. Right-click on Customers / Fields node and press New Field.

Creating a new field in Customers controller.

Assign the following values:

Property Value
Name Photo
Type Byte[]
Allow null values. yes
Value is retrieved on demand yes
Source Fields CustomerID
On Demand Handler CustomerPhotoHandler
On Demand Style Thumbnail
Label Photo

Save the field. Drag the new field node onto Customers / Views / editForm1 to instantiate a data field in the view.

Dropping the 'Photo' field node onto view 'editForm1'.     Photo data field instantiated in view editForm1.

Use the same technique to create a data field in view grid1 as well.

Next, double-click on the Customers controller node. Enter the following in BLOB Adapter Configuration.

BLOB Adapter Configuration

Field: Photo
Storage-System: File
Path-Template: C:\Northwind\Customers\{CustomerID}-{PhotoFileName}

Press OK to save changes.

Viewing the Results

On the toolbar, press Browse. Navigate to the Customers page and start editing a record. The new Photo field will accept file uploads. Click on the link and upload a file. The bar at the top of the screen will show a confirmation of upload and a thumbnail of the picture will be displayed. The File Name, Length, and Content Type utility fields will be updated accordingly.

Uploading a picture to Photo field in Customers controller.

The files can be seen in File Explorer.

The uploaded files are stored in the specified folder.

To upload files larger than 4 MB, you will need to increase the application upload size limit.