How to use a FireDAC TFDConnection to iterate through tables, fields and field definitions - sqlite

Question

I am teaching myself to use SQLite and FireDAC together in Delphi. I am not very experienced with the latest incarnations of databases and tools so after writing a very simple application to display a single table from an SQLite file, I decided that I would put together a simple viewer 'frame' that would help me learn and maybe give me (eventually) a debugging tool to put in my Application for engineering use.
So, I've used a simple TTreeView and I wish to populate it with a hierarchy of 'databases' (catalogues?), 'tables', 'field names' and 'field types'. So far it has been remarkably easy to list the catalogues, tables and fields (using TFDConnection.Getxxxxx) but I cant see how to go deeper to get field definitions. Is this possible to do from a TFDConnection? Or do I need to open a temporary query?
My existing code is shown below and my 'field types' would be a further nested loop when shown as '// xxxxxxxxxxxxxxxxxxx'
procedure TForm1.Button1Click(Sender: TObject);
procedure DatabaseToTreeView( AConnection : TFDConnection; ATreeView : TTreeView );
procedure ProcessConnection;
procedure ProcessCatalogueName( const ACatalogueName : string; ARoot : TTreeNode );
procedure ProcessTableName( const ATableName : string; ARoot : TTreeNode );
var
List : TStrings;
{Node : TTreeNode;}
I : integer;
begin
List := TStringList.Create;
try
AConnection.GetFieldNames( ACatalogueName, '', ATableName, '', List );
for I := 0 to List.Count-1 do
begin
{Node := }ATreeView.Items.AddChild( ARoot, List[I] );
// xxxxxxxxxxxxxxxxxxx
end;
finally
List.Free;
end;
end;
var
List : TStrings;
Node : TTreeNode;
I : integer;
begin
List := TStringList.Create;
try
AConnection.GetTableNames( ACatalogueName, '', '', List );
for I := 0 to List.Count-1 do
begin
Node := ATreeView.Items.AddChild( ARoot, List[I] );
ProcessTableName( List[I], Node );
end;
finally
List.Free;
end;
end;
var
List : TStrings;
Node : TTreeNode;
I : integer;
begin
List := TStringList.Create;
try
AConnection.GetCatalogNames( '', List );
if List.Count = 0 then
ProcessCatalogueName( '', nil )
else
for I := 0 to List.Count-1 do
begin
Node := ATreeView.Items.AddChild( nil, List[I] );
ProcessCatalogueName( List[I], Node );
end;
finally
List.Free;
end;
end;
begin
ATreeView.Items.Clear;
ATreeView.Items.BeginUpdate;
try
ProcessConnection;
finally
ATreeView.Items.EndUpdate;
end;
end;
begin
FDConnection1.Open;
FDQuery1.Active := true;
DatabaseToTreeView( FDConnection1, TreeView1 );
end;
Many thanks, Brian.

Answer 1

One solution is to instantiate a TFDTable, connect it to AConnection and call FieldDefs.Update. This won't fetch any data.

Answer 2

Use the TFDMetaInfoQuery component. It is unified for getting metadata information, so it's usable with any kind of supported DBMS. It populates metadata resultsets by the requested MetaInfoKind and given DBMS object description.

Answer 3

Instead of using a temporary query with a false condition to get table schema without any data (such as "select * from tablename where 1=0" - I assume that is what you meant), depending on your database, you could also use a query to get table information. Like;
For MySQL:
show columns from tablename;
For SQLite:
PRAGMA table_info(tablename)
For MS SQL Server:
select column_name, data_type, character_maximum_length from INFORMATION_SCHEMA.COLUMNS where table_name = 'tablename';
I believe PostgreSQL also has such a function, however I dont have a pgsql installation handy at this time.