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IDBSchemaRowsetImpl Class

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Provides implementation for schema rowsets.

Syntax

template <class SessionClass>
class ATL_NO_VTABLE IDBSchemaRowsetImpl : public IDBSchemaRowset

Parameters

SessionClass
The class by which IDBSchemaRowsetImpl is inherited. Typically, this class will be the user's session class.

Requirements

Header: atldb.h

Members

Methods

Name Description
CheckRestrictions Checks the validity of restrictions against a schema rowset.
CreateSchemaRowset Implements a COM object creator function for the object specified by the template parameter.
SetRestrictions Specifies which restrictions you support on a particular schema rowset.

Interface Methods

Name Description
GetRowset Returns a schema rowset.
GetSchemas Returns a list of schema rowsets accessible by IDBSchemaRowsetImpl::GetRowset.

Remarks

This class implements the IDBSchemaRowset interface and the templatized creator function CreateSchemaRowset.

OLE DB uses schema rowsets to return data about the data in a provider. Such data is often called "metadata." By default, a provider must always support DBSCHEMA_TABLES, DBSCHEMA_COLUMNS, and DBSCHEMA_PROVIDER_TYPES, as described in IDBSchemaRowset in the OLE DB Programmer's Reference. Schema rowsets are designated in a schema map. For information about the schema map entries, see SCHEMA_ENTRY.

The OLE DB Provider Wizard, in the ATL Object Wizard, automatically generates code for the schema rowsets in your project. (By default, the wizard supports the mandatory schema rowsets previously mentioned.) When you create a consumer using the ATL Object Wizard, the wizard uses schema rowsets to bind the correct data to a provider. If you do not implement your schema rowsets to provide the correct metadata, the wizard will not bind the correct data.

For information on how to support schema rowsets in your provider, see Supporting Schema Rowsets.

For more information about schema rowsets, see Schema Rowsets in the OLE DB Programmer's Reference.

IDBSchemaRowsetImpl::CheckRestrictions

Checks the validity of restrictions against a schema rowset.

Syntax

HRESULT CheckRestrictions(REFGUID rguidSchema,
   ULONG cRestrictions,  const VARIANT rgRestrictions[]);

Parameters

rguidSchema
[in] A reference to the requested schema rowset GUID (for example, DBSCHEMA_TABLES).

cRestrictions
[in] The number of restrictions that the consumer passed in for the schema rowset.

rgRestrictions
[in] An array of length cRestrictions of restriction values to be set. For more information, see the description of the rgRestrictions parameter in SetRestrictions.

Remarks

Use CheckRestrictions to check the validity of restrictions against a schema rowset. It checks restrictions for DBSCHEMA_TABLES, DBSCHEMA_COLUMNS, and DBSCHEMA_PROVIDER_TYPES schema rowsets. Call it to determine if a consumer's call to IDBSchemaRowset::GetRowset is correct. If you want to support schema rowsets other than those listed above, you should create your own function to carry out this task.

CheckRestrictions determines if the consumer is calling GetRowset with the correct restriction and the correct restriction type (for example, a VT_BSTR for a string) that the provider supports. It also determines if the correct number of restrictions are supported. By default, CheckRestrictions will ask the provider, through the SetRestrictions call, which restrictions it supports on a given rowset. It then compares the restrictions from the consumer against those supported by the provider and either succeeds or fails.

For more information on schema rowsets, see IDBSchemaRowset in the OLE DB Programmer's Reference in the Windows SDK.

IDBSchemaRowsetImpl::CreateSchemaRowset

Implements a COM object creator function for the object specified by the template parameter.

Syntax

template template <class SchemaRowsetClass>
HRESULT CreateSchemaRowset(IUnknown *pUnkOuter,
   ULONG cRestrictions,
   const VARIANT rgRestrictions[],
   REFIID riid,
   ULONG cPropertySets,
   DBPROPSET rgPropertySets[],
   IUnknown** ppRowset,
   SchemaRowsetClass*& pSchemaRowset);

Parameters

pUnkOuter
[in] An outer IUnknown when aggregating, otherwise NULL.

cRestrictions
[in] The count of restrictions applied to the schema rowset.

rgRestrictions
[in] An array of cRestrictionsVARIANTs to be applied to the rowset.

riid
[in] The interface to QueryInterface for on the output IUnknown.

cPropertySets
[in] The number of property sets to set.

rgPropertySets
[in] An array of DBPROPSET structures that specify the properties being set.

ppRowset
[out] The outgoing IUnknown requested by riid. This IUnknown is an interface on the schema rowset object.

pSchemaRowset
[out] A pointer to an instance of the schema rowset class. Typically, this parameter is not used, but it can be used if you must perform more work on the schema rowset before handing it out to a COM object. The lifetime of pSchemaRowset is bound by ppRowset.

Return Value

A standard HRESULT value.

Remarks

This function implements a generic creator for all types of schema rowsets. Typically, the user does not call this function. It is called by the implementation of the schema map.

IDBSchemaRowsetImpl::SetRestrictions

Specifies which restrictions you support on a particular schema rowset.

Syntax

void SetRestrictions(ULONG cRestrictions,
   GUID* /* rguidSchema */,
   ULONG* rgRestrictions);

Parameters

cRestrictions
[in] The number of restrictions in the rgRestrictions array and the number of GUIDs in the rguidSchema array.

rguidSchema
[in] An array of the GUIDs of the schema rowsets for which to fetch restrictions. Each array element contains the GUID of one schema rowset (for example, DBSCHEMA_TABLES).

rgRestrictions
[in] An array of length cRestrictions of restriction values to be set. Each element corresponds to the restrictions on the schema rowset identified by the GUID. If a schema rowset is not supported by the provider, the element is set to zero. Otherwise, the ULONG value contains a bit mask that represents the restrictions supported on that schema rowset. For more information on which restrictions correspond to a particular schema rowset, consult the table of schema rowset GUIDs in IDBSchemaRowset in the OLE DB Programmer's Reference in the Windows SDK.

Remarks

The IDBSchemaRowset object calls SetRestrictions to determine which restrictions you support on a particular schema rowset (it is called by GetSchemas through an upcasted pointer). Restrictions allow consumers to fetch only matching rows (for example, find all the columns in the table "MyTable"). Restrictions are optional, and in the case in which none are supported (the default), all data is always returned.

The default implementation of this method sets the rgRestrictions array elements to 0. Override the default in your session class to set restrictions other than the default.

For information on implementing schema rowset support, see Supporting Schema Rowsets.

For an example of an provider that supports schema rowsets, see the UpdatePV sample.

For more information on schema rowsets, see IDBSchemaRowset in the OLE DB Programmer's Reference in the Windows SDK.

IDBSchemaRowsetImpl::GetRowset

Returns a schema rowset.

Syntax

STDMETHOD (GetRowset)(IUnknown *pUnkOuter,
   REFGUID rguidSchema,
   ULONG cRestrictions,
   const VARIANT rgRestrictions[],
   REFIID riid,
   ULONG cPropertySets,
   DBPROPSET rgPropertySets[],
   IUnknown **ppRowset);

Parameters

pUnkOuter
[in] An outer IUnknown when aggregating; otherwise NULL.

rguidSchema
[in] A reference to the requested schema rowset GUID (for example, DBSCHEMA_TABLES).

cRestrictions
[in] A count of restrictions to be applied to the rowset.

rgRestrictions
[in] An array of cRestrictionsVARIANTs that represent the restrictions.

riid
[in] The IID to request of the newly created schema rowset.

cPropertySets
[in] The number of property sets to set.

rgPropertySets
[in/out] An array of DBPROPSET structures to set on the newly created schema rowset.

ppRowset
[out] A pointer to the requested interface on the newly created schema rowset.

Remarks

This method requires the user to have a schema map in the session class. Using the schema map information, GetRowset creates a given rowset object if the rguidSchema parameter is equal to one of the map entries GUIDs. See SCHEMA_ENTRY for a description of the map entry.

See IDBSchemaRowset::GetRowset in the Windows SDK.

IDBSchemaRowsetImpl::GetSchemas

Returns a list of schema rowsets accessible by IDBSchemaRowsetImpl::GetRowset.

Syntax

STDMETHOD (GetSchema s )(ULONG * pcSchemas,
   GUID ** prgSchemas,
   ULONG** prgRest);

Parameters

pcSchemas
[out] A pointer to a ULONG that is filled with the number of schemas.

prgSchemas
[out] A pointer to an array of GUIDs that is filled with a pointer to an array of schema rowset GUIDs.

prgRest
[out] A pointer to an array of ULONGs that is to be filled with the restriction array.

Remarks

This method returns an array of all schema rowsets supported by the provider. See IDBSchemaRowset::GetSchemas in the Windows SDK.

The implementation of this function requires the user to have a schema map in the session class. Using the schema map information, it then responds with the array of GUIDs for the schemas in the map. This represents the schemas supported by the provider.

See also

Schema Rowset Classes and Typedef Classes
Supporting Schema Rowsets
SCHEMA_ENTRY
UpdatePV