Working with Blob Fields of Base Views¶

When you create a base view with fields of type blob, you can specify the “content type” of these fields.

The RESTful Web service (see section RESTful Web Service) will use the content type set to these fields to display them appropriately.

The content type of a blob field can be either a constant (e.g. application/pdf) or an expression (e.g. the value of another field of the view, the result of a function, etc.).

When you create derived views over a base view with blob fields, the content type information of the field is usually propagated to the derived views. However, that is not always possible and, in this case, the blobs are considered generic blobs without content type.

• Flatten (see section Creating Flatten Views), Join (see section Creating Join Views) and Selection (see section Creating Selection Views) views propagate the content type if the content type is a constant or if the fields involved in the expression are projected as well.

• Union (see section Creating Union Views) and Intersect views (see section Creating Intersection Views) propagate the content type only if:

  • The content type is a constant and is the same in all the views that form the union or the intersection.

  • Or, it is an expression but is equivalent in all the views that form the union or the intersection.

• Minus views (see section Creating Minus Views) only propagate the content type of the first view.

• Interface views (see section Creating Interface Views) always propagate the content type.

To set the content type of a blob field, click the button beside the name of the type. Then, the Tool will open the “Field Content Type” dialog.

To enter a constant, clear the Use an expression check box and enter the value in the box in the top of the dialog.

To enter an expression, select the Use an expression check box and enter the expression in the box below.

This expression can use any field of the view.

Setting the content type of a blob field¶

The JDBC driver makes the content type of blob fields available to client applications.