* fcl-db sqldb: cosmetic; added info to readme.txt

git-svn-id: trunk@23123 -

packages/fcl-db/src/sqldb/readme.txt

@@ -1,11 +1,14 @@
-SQLDB readme file, 20 Aug 2005, Joost van der Sluis
+SQLDB readme file, initially by Joost van der Sluis
 
-since there is no real documentation about sqldb yet, this should be regarded as
-a small reminder to myself, and to others who want to write their own
-connections.
+Since there is no real documentation about sqldb yet, this should be regarded as
+the beginning of documentation for writing your own connections as well as modifying the code.
 
-From the TSQLConnection point-of-view the following methods are called if a
-select-statement is used:
+Code flow
+=========
+
+** Select statement
+From the TSQLConnection point of view the following methods are called if a
+select statement is used:
 
 OPEN:
   Prepare: (is only called when prepared is false)
@@ -15,7 +18,7 @@ OPEN:
             - Execute
             - AddFieldDefs (only if called for the first time after a prepare)
 
-GETNEXTPAKCET: (probably called several times, offcourse)
+GETNEXTPACKET: (probably called several times, of course)
             - Fetch
             - Loadfield
 
@@ -23,6 +26,7 @@ CLOSE:
             - FreeFieldBuffers
             - UnPrepareStatement (Only if prepare is False, thus if prepared queries
                          were not supported)
+												 
 UnPrepare:
             - UnPrepareStatement
             
@@ -30,8 +34,9 @@ DESTROY:
             - DeAllocateCursorHandle (Also called if the Connection is changed)
             
 
-From the TSQLConnection point-of-view the following methods are called if a non-
-select-statement is used (execsql):
+** Non select statement (execsql)
+From the TSQLConnection point of view the following methods are called if a non-
+select statement is used (execsql):
 
 Prepare: (is only called when prepared is false)
             - AllocateCursorHandle (only if the cursor <> nil)
@@ -42,7 +47,6 @@ Execute:
             - UnPrepareStatement (Only if prepare is False, thus if prepared queries
                          were not supported)
 
-
 UNPREPARE:
             - UnPrepareStatement
 
@@ -50,32 +54,85 @@ DESTROY:
             - DeAllocateCursorHandle (Also called if the Connection is changed)
 
 
-A short description of what each method in a TSQLConnection should do:
+Writing your own T*Connection
+=============================
 
-* Function AllocateCursorHandle : TSQLCursor; override;
+** Required methods
+A short description of what some methods in a TSQLConnection must do:
 
+* Function AllocateCursorHandle : TSQLCursor; override;
 This function creates and returns a TSQLcursor which can be used by any query
-for the used type of database. The cursor is only database-dependent, it is
-deallocated when the connection of the query changes, or if the query is
-destroyed.
+for the used type of database. The cursor is strictly database-dependent
+It is deallocated:
+- when the connection of the query changes, or
+- if the query is destroyed.
 
 * Procedure DeAllocateCursorHandle(var cursor : TSQLCursor); override;
-
 This function deallocates the TSQLCursor, and sets its value to nil.
 
-* procedure PrepareStatement(cursor: TSQLCursor;ATransaction : TSQLTransaction;buf : string; AParams : TParams); override;
+* Function AllocateTransactionHandle : TSQLHandle; virtual; abstract;
+*** to do ***
+
+* function GetTransactionHandle(trans : TSQLHandle): pointer; virtual; abstract;
+*** to do ***
+
+* function Commit(trans : TSQLHandle) : boolean; virtual; abstract;
+This function commits the statement in the context of 
+transaction trans.
+
+* function RollBack(trans : TSQLHandle) : boolean; virtual; abstract;
+This function rolls back/reverts the statement in the context of 
+transaction trans
+
+* function StartdbTransaction(trans : TSQLHandle; aParams : string) : boolean; virtual; abstract;
+This function starts the transaction trans.
 
+* procedure CommitRetaining(trans : TSQLHandle); virtual; abstract;
+This procedure commits the transaction tran and immediately starts the transaction again 
+(or opens a new transaction with the same parameters/settings as tran).
+
+* procedure RollBackRetaining(trans : TSQLHandle); virtual; abstract;
+This procedure rolls back the transaction tran and immediately opens a
+new transaction with the same parameters/settings as the original transaction.
+
+* procedure UpdateIndexDefs(IndexDefs : TIndexDefs;TableName : string); virtual;
+*** to do ***
+
+* procedure AddFieldDefs(cursor: TSQLCursor; FieldDefs : TfieldDefs); virtual; abstract;
+*** to do ***
+
+* function LoadField(cursor : TSQLCursor;FieldDef : TfieldDef;buffer : pointer; out CreateBlob : boolean) : boolean; virtual; abstract;
+*** to do ***
+
+* procedure LoadBlobIntoBuffer(FieldDef: TFieldDef;ABlobBuf: PBufBlobField; cursor: TSQLCursor; ATransaction : TSQLTransaction); virtual; abstract;
+*** to do ***
+
+* procedure PrepareStatement(cursor: TSQLCursor;ATransaction : TSQLTransaction;buf : string; AParams : TParams); override;
 This functions prepares the query which is given in buf.
+It's only called if Prepared is True (and cursor FPrepared is False).
 
-It's only called if Prepared is True.
-If the database supports prepared queries for the kind of sql-statement (in
-cursor.FStatementType) and the prepare was successfully, then cursor.FPrepared
-is set to True, so that prepare will not be called again, until UnPrepared
-is called. (which sets FPrepared to False)
+If the database supports prepared queries for the kind of SQL statement indicated 
+in cursor.FStatementType and the prepare was successful, then cursor.FPrepared
+is set to True. This keeps Prepare from being called again until UnPrepared
+is called (which sets FPrepared to False).
+
+* procedure UnPrepareStatement(cursor : TSQLCursor); virtual; abstract;
+This procedure sets cursor.FPrepared to false and performs cleanup tasks to
+unprepare the query statement.
 
 * procedure FreeFldBuffers(cursor : TSQLCursor); override;
+This procedure is called if a Select query is closed. This procedure is used to
+handle all actions which are needed to close a select statement.
+
+* procedure Execute(cursor: TSQLCursor;atransaction:tSQLtransaction; AParams : TParams); virtual; abstract;
+Tells the database to execute the statement. No data are loaded from the database client library into the sqldb data set buffers.
 
-This procedure is called if a Select-query is closed. This procedure is used to
-handle all actions which are needed to close a select-statement.
+* function Fetch(cursor : TSQLCursor) : boolean; virtual; abstract;
+Retrieves some resultset data from the database client library and stores them in sqldb dataset buffers.
 
+** Optional (but recommended) methods
+* function GetConnectionInfo(InfoType:TConnInfoType): string; virtual;
+Returns metadata information about server and client/driver type, version.
 
+* function GetSchemaInfoSQL(SchemaType : TSchemaType; SchemaObjectName, SchemaPattern : string) : string; virtual;
+Returns an SQL string that retrieves metadata about tables, columns, etc.