In order for ERPConnect Services to utilize a custom function module (e.g. Z_XTRACT_IS_TABLE) instead of the standard SAP function module to avoid restrictions by reading SAP tables, you will use the CustomFunction property of the ExecuteTableQuerySettings class.
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Table Restrictions
In the section Table restrictions you can find more information about the restrictions and how to install the custom function module Z_XTRACT_IS_TABLE to avoid them.