MapGuide RFC 78 - Add transaction support to FeatureService

This page contains an change request (RFC) for the MapGuide Open Source project. More MapGuide RFCs can be found on the RFCs page.

Status

RFC Template Version	(1.0)
Submission Date	(Date/Time submitted)
Last Modified	(Klain Qin) (Thu Jul 9 22:18:19 2009)
Author	(Klain Qin)
RFC Status	(draft)
Implementation Status	(not ready for review)
Proposed Milestone	(2.2)
Assigned PSC guide(s)	(Tom Fukushima)
Voting History	(vote date)
+1
+0
-0
-1
no vote

Overview

This proposal is to enhance the transaction capability of MapGuide Feature Service to support executing not only a sequence of standard commands(delete/update/insert) but also a sequence of sql statements within a single transaction.

Motivation

Currently MapGuide Feature Service supports executing a sequence of standard commands within a single transaction through the API illustrated below. The standard commands are delete/update/insert. If you pass in true for useTransaction, the API will start a transaction and commit(or rollback) it at the end. Thus all command execution will reside inside a single transaction.

virtual MgPropertyCollection* UpdateFeatures( MgResourceIdentifier* resource,
                                              MgFeatureCommandCollection* commands,
                                              bool useTransaction ) = 0;

However, MapGuide Feature Service also provides another two APIs to execute sql statements as illustrated below, where a database transaction will internally be started and committed befor and after the sql statement execution. Here the capability of executing a sequence of sql statements within a single transaction is missing.

virtual INT32 ExecuteSqlNonQuery( MgResourceIdentifier* resource,
                                  CREFSTRING sqlNonSelectStatement ) = 0;
virtual MgSpatialContextReader* GetSpatialContexts( MgResourceIdentifier* resource,
                                                    bool bActiveOnly) = 0;

This proposal is to extend Feature Service to support executing a sequence of sql statements within a single transaction.

Proposed Solution

A new class of MgTransaction will be added to represent a transaction to be performed in a data store.

/// \brief
/// MgTransaction represents a transaction to be performed in a DataStore.
/// If the transaction is time out, commit or rollback a transaction will
/// result in one exception MgFeatureServiceException thrown.
class MgTransaction : public MgGuardDisposable
{
PUBLISHED_API:
    /// \brief
    /// Commit the transaction.
    ///
    virtual void Commit() = 0;

    /// \brief
    /// Rollback the transaction.
    ///
    virtual void Rollback() = 0;

    /// \brief
    /// Get the identifier of feature source associated with the transaction.
    ///
    /// \return
    /// Returns the identifier of feature source associated with the transaction.
    ///
    virtual MgResourceIdentifier* GetFeatureSource() = 0;
};

Changes to Feature Service

/// \brief
/// Provides an abstraction layer for the storage and retrieval
/// of feature data in a technology-independent way. The API
/// lets you determine what storage technologies are available
/// and what capabilities they have. Access to the storage
/// technology is modeled as a connection. For example, you can
/// connect to a file and do simple insertions or connect to a
/// relational database and do transaction-based operations.
class MgFeatureService : public MgService 
{
PUBLISHED_API:
    /// \brief
    /// Begins a transaction and return it.
    ///
    /// \param resource (MgResourceIdentifier)
    /// A resource identifier referring to a feature source.
    ///
    /// \return
    /// Returns an MgTransaction instance.
    ///
virtual MgTransaction* BeginTransaction(MgResourceIdentifier* resource) = 0;
};

One example using the new API

MgTransaction tran = AcMapFeatureService::StartTransaction(resourceId);
AcMapFeatureService::ExecuteSql(resourceId, sql statement1); 
AcMapFeatureService::ExecuteSql(resourceId, sql statement2); 
AcMapFeatureService::UpdateFeatures(resourceId, standard commands, false);  // NOTE: you have to pass in false for useTransaction here.
tran->Commit() // or tran->Rollback(); 

Implications

This section allows discussion of the repercussions of the change, such as whether there will be any breakage in backwards compatibility, if documentation will need to be updated, etc.

Test Plan

How the proposed change will be tested, if applicable. New unit tests should be detailed here???

Funding/Resources

This section will confirm that the proposed feature has enough support to proceed. This would typically mean that the entity making the changes would put forward the RFC, but a non-developer could act as an RFC author if they are sure they have the funding to cover the change.