Read FieldCount to determine the number of entries in the field map. Used with the Fields property, this is useful for applications that need to iterate over all of the mapped fields.  

FieldCount is the same as the number of columns in the TCustomDBGrid. The field map can contain undefined fields, which do not appear in the dataset. Undefined fields in the field map stand in for fields in the columns of the grid that are not in the dataset, such as calculated fields. 

AddMapping 

DataSet 

Fields 

SparseMap