Use the CheckUpdatable property value to control, should AnyDAC or not to raise an exception, when application tries to modify field value in an inappropriate state. The default value is True. 

This is normally prohibited when:

• dataset is not in dsEdit, dsInsert, dsSetKey, dsCalcFields, dsFilter, dsNewValue, dsInternalCalc state;
• dataset state is dsEdit, dsInsert and TField has ReadOnly = True and CheckReadOnly = True;
• dataset state is dsSetKey and field is not indexed.

The exception will be raised when CheckUpdatable is True and one of the above conditions is not met.

property CheckUpdatable: Boolean;

Editing the Data, TField.ReadOnly, CheckReadOnly, CheckRequired