Vincoli OLE DB (SQL Server Compact)

Microsoft SQL Server Compact 3.5 (SQL Server Compact 3.5) supporta vincoli per l'attivazione di regole di integrità dei dati in un database.

Utilizzo dei vincoli

I vincoli vengono aggiunti alle colonne mediante l'interfaccia ITableDefinitionWithConstraints. Per i vincoli di chiave esterna, l'elemento matchType della struttura DBCONSTRAINTDESC deve essere sempre impostato su DBMATCHTYPE_FULL.

Nota

Il motore di database di SQL Server Compact 3.5 impone alcune limitazioni relativamente ai tipi di vincoli e al relativo funzionamento. Per ulteriori informazioni, vedere Informazioni sui database (SQL Server Compact).

Esempi

Nell'esempio seguente viene illustrato come utilizzare OLE DB per aggiungere un nuovo vincolo UNIQUE alla colonna Extension della tabella Employees mediante il metodo ITableDefinitionWithConstraints::AddConstraint.

// 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;