OLE DB-Einschränkungen (SQL Server Compact)

Microsoft SQL Server Compact 3.5 (SQL Server Compact 3.5) unterstützt Einschränkungen, mit denen in einer Datenbank Regeln zur Datenintegrität erzwungen werden können.

Verwenden von Einschränkungen

Einschränkungen werden Spalten über die ITableDefinitionWithConstraints-Schnittstelle hinzugefügt. Für FOREIGN KEY-Einschränkungen sollte das matchType-Element der DBCONSTRAINTDESC-Struktur immer auf DBMATCHTYPE_FULL festgelegt sein.

Beispiele

Im folgenden Beispiel wird gezeigt, wie der Extension-Spalte der Employees-Tabelle mit OLE DB eine neue UNIQUE-Einschränkung hinzugefügt werden kann, indem die ITableDefinitionWithConstraints::AddConstraint-Methode verwendet wird.

// Declarations
HRESULT                         hr;
DBID                            TableName;  // name of table for new constraint
DBID                            ColumnList[1]; // name of column for new constraint
DBID                            ConstraintName; // name of new constraint
DBPROP                          dbprop[1];
DBPROPSET                       dbpropset[1];
DBCONSTRAINTDESC                rgConstraintDescs[1]; // Structure for constraint properties
IDBInitialize                   *pIDBInitialize       = NULL;        
IDBProperties                   *pIDBProperties       = NULL;        
IDBCreateSession                *pIDBCreateSession    = NULL;
ITableDefinitionWithConstraints *pITbleDefWithConstrt = NULL; // supports adding constraints

if (FAILED(hr = CoInitialize(NULL)))
{
    return;
}

VariantInit(&dbprop[0].vValue);        

// Create an instance of the OLE DB Provider
hr = CoCreateInstance(    CLSID_SQLSERVERCE, 0, CLSCTX_INPROC_SERVER,
    IID_IDBInitialize, (void**)&pIDBInitialize);
if(FAILED(hr))
{
    goto Exit;
}

// Initialize a property with name of database
// Open an exsiting database myDatabase
dbprop[0].dwPropertyID     = DBPROP_INIT_DATASOURCE;
dbprop[0].dwOptions         = DBPROPOPTIONS_REQUIRED;
dbprop[0].vValue.vt         = VT_BSTR;
dbprop[0].vValue.bstrVal = L"\\windows\\MyDB.sdf";

// Initialize the property set
dbpropset[0].guidPropertySet = DBPROPSET_DBINIT;
dbpropset[0].rgProperties     = dbprop;
dbpropset[0].cProperties     = sizeof(dbprop)/sizeof(dbprop[0]);

//Set initialization properties.
hr = pIDBInitialize->QueryInterface(IID_IDBProperties, 
    
(void **)&pIDBProperties);
if(FAILED(hr))
{
    goto Exit;
}

// Sets properties in the Data Source and initialization property groups
hr = pIDBProperties->SetProperties(1, dbpropset); 
if(FAILED(hr))
{
    goto Exit;
}

// Initializes a data source object 
hr = pIDBInitialize->Initialize();
if(FAILED(hr))
{
    goto Exit;
}

// Get IDBCreateSession interface
hr = pIDBInitialize->QueryInterface(IID_IDBCreateSession,
    (void**)&pIDBCreateSession);
if (FAILED(hr))
{
    //Send error-specific message and do error handling
    goto Exit;
}

// Create a session object. 
hr = pIDBCreateSession->CreateSession(NULL, IID_ITableDefinitionWithConstraints, 
    (IUnknown**) &pITbleDefWithConstrt);

// (This sample assumes that we have information about the Employees table
// database schema.)
// Prepare the table name DBID as Employees.
TableName.eKind          = DBKIND_NAME;
TableName.uName.pwszName = L"Employees";

// Prepare the list of columns that will receive the UNIQUE constraint. 
// In this case, just the Extension column. 
ColumnList[0].eKind = DBKIND_NAME;
ColumnList[0].uName.pwszName = L"Extension";

// Build the DBCONSTRAINTDESC structure needed to make the 
// ITableDefinitionWithConstraints::AddConstraint 
// call to add the constraint. 
rgConstraintDescs[0].pConstraintID = &ConstraintName;
rgConstraintDescs[0].ConstraintType = DBCONSTRAINTTYPE_UNIQUE;
rgConstraintDescs[0].cColumns = 1;
rgConstraintDescs[0].rgColumnList = ColumnList;
rgConstraintDescs[0].Deferrability = 0;  // Constraints are not deferrable.
// The following properties are not used in UNIQUE constraints
rgConstraintDescs[0].pReferencedTableID = NULL;
rgConstraintDescs[0].cForeignKeyColumns = 0;
rgConstraintDescs[0].rgForeignKeyColumnList = NULL;
rgConstraintDescs[0].pwszConstraintText = NULL;
rgConstraintDescs[0].UpdateRule = DBUPDELRULE_NOACTION;
rgConstraintDescs[0].DeleteRule = DBUPDELRULE_NOACTION;
rgConstraintDescs[0].MatchType = DBMATCHTYPE_NONE;

// Add the new constraint
hr = pITbleDefWithConstrt->AddConstraint(&TableName, rgConstraintDescs);

Exit: 

// When finished, clear the properties arrays and release interfaces.
// Uninitialize the environment.

Return;