The 'Key expression is undefined' error occurs when you use LinqServerModeDataSource / EntityServerModeDataSource

• Feb 15, 2022

Error Description:

This error can occur when the LinqServerModeDataSource / EntityServerModeDataSource data sources cannot automatically recognize the key (unique) column from the TableName or QueryableSource specified at runtime.

Solution:

Do the following to resolve this issue:

• Handle the Selecting/Selecting event.

• Specify the e.KeyExpression property.

C#

protected void LinqServerModeDataSourceInstance_Selecting(object sender, DevExpress.Data.Linq.LinqServerModeDataSourceSelectEventArgs e) {  
    e.KeyExpression = UNIQUE_KEY_COLUMN_NAME;  
}  

VB.NET

Protected Sub LinqServerModeDataSourceInstance_Selecting(ByVal sender As Object, ByVal e As DevExpress.Data.Linq.LinqServerModeDataSourceSelectEventArgs)  
    e.KeyExpression = UNIQUE_KEY_COLUMN_NAME  
End Sub