How to sort with a CASE statement in an EntityDataSource?

问题:

I'm using a CASE statement in my EntityDataSource to do custom sorting. Consider the following code:

<asp:EntityDataSource ID="myEntityDataSource" runat="server"      ConnectionString="name=MySQLEntities1"      DefaultContainerName="MySQLEntities1"      EnableFlattening="False"      EntitySetName="Persons"      EntityTypeFilter="Persons"     OrderBy="it.[Pack],               CASE it.[Type]                  WHEN 'MAN' THEN 1                  WHEN 'VROUW' THEN 2                  WHEN 'KIND' THEN 3               END,               it.[BirthDate] ASC" /> 

In T-SQL this would be a perfecty normal way of sorting, but used in the EntityDataSource it throws the following exception:

The query syntax is not valid. Near identifier 'it', line 11, column 21.

How can I get this type of sorting to work in my EntityDataSource?

回答1:

I was trying the very same thing today. I discovered on the Entity SQL Reference site that you apparently have to use CASE WHEN and cannot use CASE [value] WHEN. This approach, although not as it would be in T-SQL, did work for me. So your code should look like this:

<asp:EntityDataSource ID="myEntityDataSource" runat="server"  ConnectionString="name=MySQLEntities1"       DefaultContainerName="MySQLEntities1"       EnableFlattening="False"       EntitySetName="Persons"       EntityTypeFilter="Persons"      OrderBy="it.[Pack],                CASE  WHEN it.[Type] = 'MAN' THEN 1                   WHEN it.[Type] = 'VROUW' THEN 2                   WHEN it.[Type] = 'KIND' THEN 3 END, it.[BirthDate] ASC" /> 

MSDN Entity SQL Reference: 'CASE'

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