Convert type (String to TField)

[Lygedas]

Hello,

I collide with one problem which I very need to solve.
In Table1 field A (type is string) I have value : "Table2.FieldByName("B")".
So I want :

var
Field1, Field3 : String;
Field2 : TField;

begin
Field1 : = Table1.FieldByName("A").Text;
Field2 : = (here I want to convert string type to TField type)
?????????????????????????
Field3 : = Field2.Value;
Print Field3; 'I must see Table2 field B value
end.

I will be very appreciate in your help.

Thanks.

Lygedas

[Wayne Niddery (TeamB)]

Lygedas wrote in message <81bu4d$5n...@forums.borland.com>...

>
>I collide with one problem which I very need to solve.
>In Table1 field A (type is string) I have value :
"Table2.FieldByName("B")".
>So I want :
>
>var
> Field1, Field3 : String;
> Field2 : TField;
>
>begin
> Field1 : = Table1.FieldByName("A").Text;
> Field2 : = (here I want to convert string type to TField type)
>?????????????????????????
> Field3 : = Field2.Value;
> Print Field3; 'I must see Table2 field B value
>end.

You cannot "execute" a string as if it were compiled code. You will need to
parse this yourself. I would recommend storing it as "Table2.B" then it's
easier to use string routines to break this out:

var
Field1, Field3 : String;
tablename, fieldname: string;
table: TTable;
begin
Field1 : = Table1.FieldByName("A").Text; // gets 'Table2.B'
tablename := Copy(Field1, 1, Pos('.', Field1) - 1);
fieldname := Copy(Field1, Pos('.', Field1) + 1, 255);
// next line assumes you actually have a TTable
// component on the form called Table2
table := FindComponent(tablename);
Field3 := table.FieldByName(fieldname).AsString;
end;

--
Wayne Niddery - WinWright Consulting
RADBooks - http://members.home.net/wniddery/
Toronto Delphi Users Group - http://www.tdug.com/

[Jaroslavas Akmanovas]

When I try to built, I receive message :
Incompatible types: 'TTable' and 'TComponents'

Thanks

Wayne Niddery (TeamB) wrote in message <81ccpa$8i...@forums.borland.com>...

[Keith Johnson]

Jaroslavas Akmanovas <jaroslavas...@intelsoftas.lt> wrote in message
news:81dm82$go...@forums.borland.com...

> When I try to built, I receive message :
> Incompatible types: 'TTable' and 'TComponents'

> > table := FindComponent(tablename);

Just typecast->
table:=TTable(FindComponent(tablename));

Keith..

[samueld...@gmail.com]

On Monday, November 22, 1999 12:00:00 AM UTC-8, Lygedas wrote:
> Hello,

>
> I collide with one problem which I very need to solve.
> In Table1 field A (type is string) I have value : "Table2.FieldByName("B")".
> So I want :
>
> var
> Field1, Field3 : String;
> Field2 : TField;
>
> begin
> Field1 : = Table1.FieldByName("A").Text;
> Field2 : = (here I want to convert string type to TField type)
> ?????????????????????????
> Field3 : = Field2.Value;
> Print Field3; 'I must see Table2 field B value
> end.
>

> I will be very appreciate in your help.
>
> Thanks.
>
> Lygedas

from Sam D. Hunt
You actually need three array structs to do what you are attempting.
using the following arrays... (see below arrays for continuation)

ARRAY 1:
FieldTypes: array [TFieldType] of String =
('ftUnknown', 'ftString', 'ftSmallint', 'ftInteger', 'ftWord', 'ftBoolean',
'ftFloat', 'ftCurrency', 'ftBCD', 'ftDate', 'ftTime', 'ftDateTime', 'ftBytes', 'ftVarBytes',
'ftAutoInc', 'ftBlob', 'ftMemo', 'ftGraphic', 'ftFmtMemo', 'ftParadoxOle', 'ftDBaseOle',
'ftTypedBinary', 'ftCursor', 'ftFixedChar', 'ftWideString', 'ftLargeint', 'ftADT', 'ftArray',
'ftReference', 'ftDataSet', 'ftOraBlob', 'ftOraClob', 'ftVariant', 'ftInterface', 'ftIDispatch',
'ftGuid', 'ftTimeStamp', 'ftFMTBcd', 'ftFixedWideChar', 'ftWideMemo', 'ftOraTimeStamp',
'ftOraInterval', 'ftLongWord', 'ftShortint', 'ftByte', 'ftExtended', 'ftConnection',
'ftParams', 'ftStream', 'ftTimeStampOffset', 'ftObject', 'ftSingle');

ARRAY 2:
sFieldTypes: array [1..52] of String =
('ftUnknown', 'ftString', 'ftSmallint', 'ftInteger', 'ftWord', 'ftBoolean',
'ftFloat', 'ftCurrency', 'ftBCD', 'ftDate', 'ftTime', 'ftDateTime', 'ftBytes', 'ftVarBytes',
'ftAutoInc', 'ftBlob', 'ftMemo', 'ftGraphic', 'ftFmtMemo', 'ftParadoxOle', 'ftDBaseOle',
'ftTypedBinary', 'ftCursor', 'ftFixedChar', 'ftWideString', 'ftLargeint', 'ftADT', 'ftArray',
'ftReference', 'ftDataSet', 'ftOraBlob', 'ftOraClob', 'ftVariant', 'ftInterface', 'ftIDispatch',
'ftGuid', 'ftTimeStamp', 'ftFMTBcd', 'ftFixedWideChar', 'ftWideMemo', 'ftOraTimeStamp',
'ftOraInterval', 'ftLongWord', 'ftShortint', 'ftByte', 'ftExtended', 'ftConnection',
'ftParams', 'ftStream', 'ftTimeStampOffset', 'ftObject', 'ftSingle');

ARRAY 3:
ftFieldTypes: array [1..52] of TFieldType =
(ftUnknown, ftString, ftSmallint, ftInteger, ftWord, ftBoolean,
ftFloat, ftCurrency, ftBCD, ftDate, ftTime, ftDateTime, ftBytes, ftVarBytes,
ftAutoInc, ftBlob, ftMemo, ftGraphic, ftFmtMemo, ftParadoxOle, ftDBaseOle,
ftTypedBinary, ftCursor, ftFixedChar, ftWideString, ftLargeint, ftADT, ftArray,
ftReference, ftDataSet, ftOraBlob, ftOraClob, ftVariant, ftInterface, ftIDispatch,
ftGuid, ftTimeStamp, ftFMTBcd, ftFixedWideChar, ftWideMemo, ftOraTimeStamp,
ftOraInterval, ftLongWord, ftShortint, ftByte, ftExtended, ftConnection,
ftParams, ftStream, ftTimeStampOffset, ftObject, ftSingle);

FIRST Step (using array 1):GET string name of the target TFieldType
sString := FieldTypes[MyTable.Fields[{field number}].DataType];

SECOND Step(using second array):
Step through sFieldTypes array until you find the value equal to sString in step 1.
Capture the sFieldTypes index in an integer, such as iIndex.

LAST Step (using array 3):
Your sString string value can be converted back to the original TFieldType thusly:

TFieldType := ftFieldTypes[iIndex];

This works great for me.
I use this strategy to get the field info from a table on a remote server over the internet and create a local copy in a TClientDataset. I then use the local client dataset to update the remote server using Indy 10 TCP client and server components. The only issue I haven't fully resolved is concurrency.

Good luck.
Sam Hunt

[samueld...@gmail.com]

On Monday, November 22, 1999 12:00:00 AM UTC-8, Lygedas wrote:
> Hello,
>
> I collide with one problem which I very need to solve.
> In Table1 field A (type is string) I have value : "Table2.FieldByName("B")".
> So I want :
>
> var
> Field1, Field3 : String;
> Field2 : TField;
>
> begin
> Field1 : = Table1.FieldByName("A").Text;
> Field2 : = (here I want to convert string type to TField type)
> ?????????????????????????
> Field3 : = Field2.Value;
> Print Field3; 'I must see Table2 field B value
> end.
>
> I will be very appreciate in your help.
>
> Thanks.
>
> Lygedas

ok. so no one has read my post, yet. good. it had a couple of small errors.
array 2 and 3 should have been indexed 0..51, not 1..52. my strategy works either way, but 0..51 more properly describes the array indices.

Improvement...
I suggested searching for string found in step one in the second array.
Instead of...

sFieldTypes: array [1..52] of String =
('ftUnknown', 'ftString', 'ftSmallint', 'ftInteger', 'ftWord', 'ftBoolean',
'ftFloat', 'ftCu

...

I suggest using this array...
iFieldTypes: array [TFieldType] of String =
('0', '1', '2', '3', '4', '5',
'6', '7', '8', '9', '10', '11', '12', '13',
'14', '15', '16', '17', '18', '19', '20',
'21', '22', '23', '24', '25', '26', '27',
'28', '29', '30', '31', '32', '33', '34',
'35', '36', '37', '38', '39', '40',
'41', '42', '43', '44', '45', '46',
'47', '49', '50', '51');

then in step two, you don't need to step through the array to find a "ftString".
Instead of searching for "ftString", you will be converting "1".
In the array...

FieldTypes: array [TFieldType] of String =
('ftUnknown', 'ftString', 'ftSmallint', 'ftInteger', 'ftWord', 'ftBoolean',
'ftFloat', 'ftCurrency', 'ftBCD', 'ftDate', 'ftTime', 'ftDateTime', 'ftBytes', 'ftVarBytes',
'ftAutoInc', 'ftBlob', 'ftMemo', 'ftGraphic', 'ftFmtMemo', 'ftParadoxOle', 'ftDBaseOle',
'ftTypedBinary', 'ftCursor', 'ftFixedChar', 'ftWideString', 'ftLargeint', 'ftADT', 'ftArray',
'ftReference', 'ftDataSet', 'ftOraBlob', 'ftOraClob', 'ftVariant', 'ftInterface', 'ftIDispatch',
'ftGuid', 'ftTimeStamp', 'ftFMTBcd', 'ftFixedWideChar', 'ftWideMemo', 'ftOraTimeStamp',
'ftOraInterval', 'ftLongWord', 'ftShortint', 'ftByte', 'ftExtended', 'ftConnection',
'ftParams', 'ftStream', 'ftTimeStampOffset', 'ftObject', 'ftSingle');

the field type is then FieldTypes[strtoint('1')].
no stepping or looping.
This has to be faster and is definitely more elegant.
Sam Hunt

[lionel...@gmail.com]

or a simplest way :

Field2.DataType := TFieldType(GetEnumValue(TypeInfo(TFieldType),Field2));