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Nice in theory, not really doable though - they are all so different because we all have different ideas.

Also have something alike here Haven't tested with something newer than XE2 though

In general, you can't losslessly map a wider set of values to a tight one (well, thanks Cap'n Obvious). Integer is MinInt..MaxInt and JSON value is MinInt..MaxInt + null + undefined/non-existing. So you either got to make assumptions based on subject (f.e.x, if you're reading naturals - -1 could indicate any missing/invalid value) or to check actual value before each assignment (if JSONDoc.GetValue(..)).

Which Database system do you use? Which connection components? If the field in the database is declared as "Integer", it should never contain a Space character. It could be NULL, which means it doesn't contain any value. Most database access components will translate NULL to the value 0, so an empty field should not raise an exception. Which value do you expect in case the field is NULL? To be save, you can test for empty fields yourself: var F : TField; F := Qry.FindField('IntegerField'); if Assigned(F) and (not F.IsNull) then aObject.IntValue := F.AsInteger else aObject.IntValue := -1; // or whatever value you choose in case of an empty field.