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

aspnet-403755-troubleshooting-server-side-issues-key-expression-is-undefined-linqservermodedatasource-entityservermodedatasource.md

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Original Source

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

  • Sep 27, 2023

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:

csharp
protected void LinqServerModeDataSourceInstance_Selecting(object sender, DevExpress.Data.Linq.LinqServerModeDataSourceSelectEventArgs e) {  
    e.KeyExpression = UNIQUE_KEY_COLUMN_NAME;  
}
vb
Protected Sub LinqServerModeDataSourceInstance_Selecting(ByVal sender As Object, ByVal e As DevExpress.Data.Linq.LinqServerModeDataSourceSelectEventArgs)  
    e.KeyExpression = UNIQUE_KEY_COLUMN_NAME  
End Sub