IRowset::GetNextRows fetches a sequence of rows. The provider maintains a next fetch position that is used in subsequent calls to either. MSDN Library The topic you requested is included in another documentation set. See IRowset::RestartPosition in the OLE DB Programmer's Reference. IRowset is the base rowset interface. It provides methods for fetching rows sequentially, getting the data from those rows, and managing rows. The topic you requested is included in another documentation set. The wizard- generated rowset object implements IAccessor, IRowset, and IRowsetInfo.
A data source consists of the data, its associated database irowset msdn s system DBMSthe platform on which the DBMS exists, and the network used to access that platform. OLE facilitates application integration by defining a set of standard interfaces, groupings of semantically related functions through which one application accesses the services of another.
Interfaces are the binary standard for component object interaction. Each interface contains a set of functions that define a contract between the object implementing the interface and the client using it. Each interface consists of a set of related methods. Each data provider will implement some subset of these interfaces. An interface in OLE is a set of related methods. A single OLE object may support multiple interfaces at the same time.
The consumer of an object can move between any interfaces supported on that object by calling QueryInterface see "Interface negotiation," below. If an object supports an interface, it supports all of the methods within that interface. Thus, once the consumer has determined that a particular interface is supported, it understands how to interact with the object. New irowset msdn s that augment the functionality already supported by the existing interfaces can be added later, but methods can never be added or removed from existing interfaces.
Because an object must either support irowset msdn s or none of irowset msdn s methods within an interface, interfaces are generally factored according to functionality. For example, if an object supports reading data and does or does not support writing data, the methods for reading data and those for writing data would appear in two different interfaces. Only the objects that supported writing data would support the interface containing the methods for writing data. OLE DB makes extensive use of interface factoring.
Individually supportable functionality, such as different levels of scrollability in a result set or command preparation and irowset msdn s support, are factored into different interfaces. Each object has one or more required interfaces that encapsulate base functionality for that object and that can expose extended functionality by implementing one or more optional interfaces.
The OLE DB consumer can determine what extended functionality the provider supports by querying for these optional interfaces. IUnknown is implemented by all component objects. All other interfaces inherit, directly or indirectly, from this interface. It has three methods: QueryInterfaceAddRefand Release. Each interface is identified by a globally unique identifier GUID by which it is known at compile time. To determine if an object supports a particular interface, the client calls QueryInterface on that object.
If an object supports the requested interface, QueryInterface returns a pointer to the interface. The interface identifier IID allows the client to dynamically determine, by way of a call to IUnknown:: QueryInterfacethe capabilities of other objects and to get the pointers to needed interfaces.
Every interface that is obtained directly by calls to QueryInterface or indirectly by calls to a method that returns an interface must be released by calling video larparus Release method of that object. Reference counts are kept on each instance of a pointer to an interface that irowset msdn s derived from IUnknown. This ensures that the object is not destroyed before all references to it irowset msdn s released. OLE uses two kinds of memory: All task memory allocated by the OLE libraries and by the object irowset msdn s is allocated using either an application-supplied allocator or the default allocator provided by OLE.
The standard memory management model in COM requires that the callee allocates irowset msdn s the caller frees. OLE DB generally follows this model, except for certain cases where performance can be gained by the caller allocating and reusing the same piece of memory, or in some special cases, by the callee giving the caller pointers to callee-owned data. In this case, the caller is not allowed to write to or free the memory.
OLE DB providers can be classified as data providers and service irowset msdn s. A data provider is one that owns data and exposes it in a tabular form. Some examples are relational database systems and spreadsheets. Examples are query processors and transaction managers. A session object defines the scope of a transaction and generates rowsets from the data source.
If the provider supports commands, the session also acts as a command factory. The data source object can also support interfaces for describing schema information and irowset msdn s creating tables and indexes for providers that support that functionality. Along with the data source object, the session encapsulates the functionality of the ODBC connection. CreateSession creates a session from the data source object. There can be multiple sessions associated with a data source object.
If a provider supports building and executing queries, it exposes a command object. A command object is generated from a irowset msdn s object. The command encapsulates the general functionality of an ODBC statement in an unexecuted state.
There may be multiple commands associated with a single session. A rowset object is a shared data object that represents tabular data, such as a result set returned by executing a query. Minimally, rowsets can be generated by calling IOpenRowset:: OpenRowset on the session. All providers are required to support this minimal functionality. If the provider supports commands, rowsets are used irowset msdn s represent the results of row-returning queries.
There are a number of other methods in OLE DB, such as the schema functions, that return information google earth ipad 2 the form of a rowset. A rowset encapsulates the general functionality of an ODBC statement in the executed state. There may be multiple rowsets associated with a single session or command.
They provide recursive data source enumeration, enhanced transaction control, and extended error retrieval. Enumerator objects list the data sources and enumerators visible to that enumerator. This is similar to the information provided by SQLDataSourcesexcept that the information can be recursive.
In addition to supporting ITransactionLocal on the session, providers that support transactions can optionally support the creation of a transaction object. Transaction objects provide more advanced transaction functionality, such as the registration of transaction notifications. Unless explicitly stated otherwise, ODBC 3. For more information on mapping ODBC 1. This section describes the basic concepts and procedures defined in OLE DB, such as initializing the environment, locating and connecting to a data source, executing a command, and retrieving data from a rowset.
In both cases, irowset msdn s application:. For the complete source code listing, see Appendix A. The individual routines in this sample are described in more detail in the following sections. The flow of control is as follows:. The Driver Manager loads and directs calls to the appropriate driver. This is shown in the preceding code example.
After cinta dipantai bali mp3 OLE library is initialized, the proper data provider is loaded by the system according to its class ID, and calls are made directly to the provider. The authentication information such as user ID, password, and the name of the data source are specified as properties of the data source object by calling IDBProperties:: The method IDBInitialize:: Initialize uses the specified properties to connect to the data source.
The primary differences are:. The following code example shows a routine that initializes a data irowset msdn s object. The general flow of control is:. Properties are used in OLE DB to specify options, such as initialization information on the data source object or supported properties of a rowset, as well as to discover properties of certain objects, such as the updatability of a rowset.
The following code example shows how an application sets dholi taro song video properties on a data source object.
The code sets four properties within a single property group. The irowset msdn s source object exposes the IDBCreateSession interface through which a session object can be created. A session defines transaction scope and acts mainly as a command irowset msdn s by supporting the IDBCreateCommand interface. The execution of a row-returning command yields a rowset object. However, the connection handle in ODBC is used for establishing connections as well as scoping transactions, so irowset msdn s application must allocate and connect a separate connection handle for each concurrent transaction.
In OLE DB you can have multiple session objects on one initialized data source object, which means you can have multiple concurrent transactions without having to make multiple connections where necessary, the provider makes additional connections using the connection information provided in the initialization of the data source object.
Like the ODBC connection handle, which can have several statement handles, a session object can have several command objects. The following code example shows setting and executing a command, and retrieving a rowset. A rowset provides a standard way to work with a multiset of rows where each row contains one or more columns of data. A rowset can be obtained in several ways. The first method, supported by all providers, uses the IOpenRowset interface. IOpenRowset provides for the simple case of retrieving all the data from the table.
The ICommandProperties interface on the command can be used to specify the interfaces and properties that must be supported by the rowsets returned by ICommand:: Conceptually, rowsets are similar to result sets in ODBC; their implementation, however, is different.
At that point, the application owns the data; neither the ODBC driver nor other components have access to that data. This model works fine provided that:. OLE DB rowsets are not only designed to provide a high performance solution for the preceding scenarios but are also designed so that:. The OLE DB rowset basically takes the memory buffer out of the application and puts it in a stand-alone, shared data object.
If cRows is zero, IRowset:: ReleaseRows does not do anything. The row handles need not form a logical cluster; they may have been obtained at separate times and need not be for contiguous underlying rows. Row handles are decremented by one reference count for each time they appear in the array. This parameter is reserved for future use and should be set to a null pointer. If rgRefCounts is a null pointer, no counts are returned.
The consumer allocates, but is not required to initialize, memory for this array and passes the address of this memory to the provider. The provider returns the reference counts in the array. The consumer allocates memory for this irowset msdn s. If rgRowStatus irowset msdn s a null pointer, no row statuses are returned.
All rows were successfully released. The row was successfully released. A row had a pending change. The following errors can occur:. A row handle was invalid. The consumer encountered a recoverable, provider-specific error, such as an RPC failure when transmitting the change to a remote irowset msdn s. ReleaseRows is called on a row with an open storage object. If the consumer, on cleanup, encounters an error while releasing the row, it should release the storage object first.
ReleaseRows decreases the reference count on the specified rows. It must be called once for each time that a row was fetched. For example, if the row was fetched three times, IRowset:: ReleaseRows must be called three times.
Furthermore, if a row handle is duplicated in rghRowsthe corresponding row will have its reference count decremented by one for each time it appears in the array. If a provider doesn't support exact reference counts on rows, it should return a reference motion data of 1 while the row is active. Consumers should be aware of this behavior and should use the returned reference count for debugging purposes only; consumers should not rely on the returned reference count to indicate whether the row would survive another release.
ReleaseRows until the rowset itself is released. If a consumer calls IRowset:: When the reference count for a row decreases to zero, the row is released under the following irowset msdn s.
Subject to the rules of the current transaction, the rowset is free to discard any resources used by a row that has a reference count of zero. For example, these might include memory, locks, and original values. When the rowset actually discards these resources is provider-specific. If the row has pending changes, the row still remains valid even though its reference count is zero.
Consumers should not use the handle of a row that has a reference count of zero, even though the handle might still be valid. If IRowsetUpdate:: Update is called to transmit pending changes irowset msdn s a row with a reference count of zero to the data store, it transmits the changes of the row and releases the row and its resources if the update succeeds. Undo is called to undo the pending changes for a row with a reference count of zero, it releases the row and its resources.
Pending changes are not lost when releasing a reference count obtained from IRowsetLocate:: A provider may take its own reference count on the row handle or store the row internally until pending changes are committed or dismissed using IRowsetUpdate:: Update or IRowsetUpdate:: After the pending changes are transmitted to the data store, methods might continue to return this error.
However, the provider might have irowset msdn s implementation that recycles row handles and thereafter cannot detect the misuse.
Because provider behavior varies, consumers should not use irowset msdn s handles of released rows. If IRowset:: This method can be called irowset msdn s the rowset is in a zombie state to allow the consumer to clean up after a transaction has been committed or aborted.
Exit focus mode. In this article. The following errors can occur: Comments IRowset:: When the reference count for a row decreases to zero, the row is released under the following circumstances: See Also Reference IRowset::