(SOLVED) From TFieldType to string and the other way around

[xinyiman]

Hi guys, I don't remember how to turn a TFieldType (example ftString, ftSmallInt, etc.) into string and the other way around. What is the syntax already?

[howardpc]

Code: Pascal  [Select][+][-]

1. uses db;
2.  
3. function FieldTypeToStr(aFieldType: TFieldType): String;
4. begin
5.   Exit(Fieldtypenames[aFieldType]);
6. end;
7.  
8. function StrToFieldType(aString: String): TFieldType;
9. var
10.   ft: TFieldType;
11. begin
12.   aString := LowerCase(aString);
13.   Delete(aString, 1, 2);
14.   for ft := Low(TFieldType) to High(TFieldType) do
15.     if aString = LowerCase(Fieldtypenames[ft]) then
16.       Exit(ft);
17.   Result := ftUnknown;
18. end;

[xinyiman]

Thanks

[wp]

Like for any enumeration you can use GetEnumName and GetEnumValue from unit typinfo:

Code: Pascal  [Select][+][-]

1. uses
2.   db, typinfo;
3.  
4. function FieldTypeToString(AFieldType: TFieldType): String;
5. begin
6.   Result := GetEnumName(Typeinfo(TFieldType), integer(AFieldType));
7. end;
8.  
9. function StringToFieldType(Str: String): TFieldType;
10. begin
11.   Result := TFieldType(GetEnumValue(TypeInfo(TFieldType), str));
12. end;

If you don't want the "ft" in the converted strings you must remove them explicitly like in Howard's example.

[howardpc]

wp is helpful in drawing attention to the typinfo routines, which are applicable to any enumeration.
The drawback of a one-line StringToFieldType() routine relying on a typecast of GetEnumValue is that it is not very robust.
For instance

Code: Pascal  [Select][+][-]

1. var
2.   ft: TFieldType;
3. begin
4.   ft := StringToFieldType('ftInvalidTypeString');
5.   ..  

will lead to a runtime error, or perhaps a crash.
Sure it is programmer error, but "we all make many mistakes", as James once wrote.

[wp]

Of course this can be added:

Code: Pascal  [Select][+][-]

1. function StringToFieldType(Str: String): TFieldType;
2. var
3.   ft: Integer;
4. begin
5.   ft := GetEnumValue(TypeInfo(TFieldType), str);
6.   if (ft >= ord(Low(TFieldType))) and (ft <= ord(High(TFieldType))) then
7.     Result := TFieldType(ft)
8.   else
9.     Result := ftUnknown;
10.     // or: raise Exception.Create('Unknown field type');
11. end;