Using schema locks

Summary

The ISchemaLock interface is used to establish an exclusive lock on a dataset when changing its schema or when performing other operations that require exclusive access to the data. The ISchemaLockInfo interface is used in conjunction with ISchemaLock to supply information concerning the schema lock, such as the type of lock and the dataset to which it has been applied.

In this topic

• About schema locks
• Schema locks with personal geodatabases
• Schema locks with file and ArcSDE geodatabases
• Types of operations requiring exclusive schema locks
• Access schema lock information using ISchemaLockInfo

About schema locks

Schema locks with file and ArcSDE geodatabases

• If a lock is acquired on a feature class in a feature dataset, the lock applies to the entire feature dataset and its contents.
• Locks also apply to both sides of a relationship class. For example, if two stand-alone feature classes are related via a relationship class and an exclusive or shared lock is acquired for one feature class, the lock is also applied to the other feature class in the relationship.

Schema locks with personal geodatabases

Types of operations requiring exclusive schema locks

• Modifications to attribute domains, such as adding or removing values from a coded value domain or changing the range for range domains

• Adding or deleting a field from a feature class or object class
• Associating a class extension with a feature class
• Creating a topology, geometric network, network dataset, terrain, schematic dataset, representation, or cadastral fabric on a set of feature classes
• Any use of the IClassSchemaEdit interface
• Putting a feature class into and taking it out of load-only mode with the IFeatureClassLoad.LoadOnlyMode property
• Managing (creating, deleting, or modifying) spatial and attribute indexes

• Checks for existing exclusive or shared locks are not made before attempting to get an exclusive lock. Instead, the call to establish an exclusive lock (using the ChangeSchemaLock method) is made within a Try block. If an exclusive lock cannot be obtained, an error will be raised and reported to the user.
• The practice of demoting an exclusive schema lock to a shared lock when an error is raised, or when the lock is no longer required. In the following code example, the exclusive schema lock is demoted in the Finally block, which demotes the exclusive lock at the end of the code execution or when an error is raised.

[C#]

public void DeleteField(IObjectClass objectClass, String fieldName)
{
    // Get the field to be deleted.
    int fieldIndex=objectClass.FindField(fieldName);
    IField field=objectClass.Fields.get_Field(fieldIndex);

    // Cast to the ISchemaLock interface.
    ISchemaLock schemaLock=(ISchemaLock)objectClass;
    try
    {
        // Get an exclusive schema lock on the object class. 
        schemaLock.ChangeSchemaLock(esriSchemaLock.esriExclusiveSchemaLock);

        // Alter the class extension for the class.
        objectClass.DeleteField(field);
    }
    catch (Exception e)
    {
        // An error was raised; therefore, notify the user.
        Console.WriteLine(e.Message);
    }
    finally
    {
        // Since the Finally block is always called, the exclusive lock is demoted
        // to a shared lock after the field is deleted and after an error is raised.
        schemaLock.ChangeSchemaLock(esriSchemaLock.esriSharedSchemaLock);
    }
}

[VB.NET]

Public Sub DeleteField(ByVal objectClass As IObjectClass, ByVal fieldName As String)
    
    ' Get the field to be deleted.
    Dim fieldIndex As Integer=objectClass.FindField(fieldName)
    Dim field As IField=objectClass.Fields.Field(fieldIndex)
    
    ' Cast to the ISchemaLock interface.
    Dim schemaLock As ISchemaLock=CType(objectClass, ISchemaLock)
    
    Try
    ' Get an exclusive schema lock on the object class.
    schemaLock.ChangeSchemaLock(esriSchemaLock.esriExclusiveSchemaLock)
    
    ' Alter the class extension for the class.
    objectClass.DeleteField(field)
    Catch e As Exception
    ' An error was raised; therefore, notify the user.
    Console.WriteLine(e.Message)
    Finally
    ' Since the Finally block is always called, the exclusive lock is demoted
    ' to a shared lock after the field is deleted and after an error is raised.
    schemaLock.ChangeSchemaLock(esriSchemaLock.esriSharedSchemaLock)
    End Try
    
End Sub

Access schema lock information using ISchemaLockInfo

[C#]

public void ListSchemaLocksForObjectClass(IObjectClass objectClass)
{
    //Get an exclusive schema lock on the dataset.
    ISchemaLock schemaLock=(ISchemaLock)objectClass;

    // Get an enumerator over the current schema locks.
    IEnumSchemaLockInfo enumSchemaLockInfo=null;
    schemaLock.GetCurrentSchemaLocks(out enumSchemaLockInfo);

    // Iterate through the locks.
    ISchemaLockInfo schemaLockInfo=null;
    while ((schemaLockInfo=enumSchemaLockInfo.Next()) != null)
    {
        Console.WriteLine("{0} : {1} : {2}", schemaLockInfo.TableName,
            schemaLockInfo.UserName, schemaLockInfo.SchemaLockType);
    }
}

[VB.NET]

Public Sub ListSchemaLocksForObjectClass(ByVal objectClass As IObjectClass)
    
    'Get an exclusive schema lock on the dataset.
    Dim schemaLock As ISchemaLock=CType(objectClass, ISchemaLock)
    
    ' Get an enumerator over the current schema locks.
    Dim enumSchemaLockInfo As IEnumSchemaLockInfo=Nothing
    schemaLock.GetCurrentSchemaLocks(enumSchemaLockInfo)
    
    ' Iterate through the locks.
    Dim schemaLockInfo As ISchemaLockInfo=Nothing
    
    Do While Not schemaLockInfo Is Nothing
        Console.WriteLine("{0} : {1} : {2}", schemaLockInfo.TableName, schemaLockInfo.UserName, schemaLockInfo.SchemaLockType)
        schemaLockInfo=enumSchemaLockInfo.Next()
    Loop
    
End Sub

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To use the code in this topic, reference the following assemblies in your Visual Studio project. In the code files, you will need using (C#) or Imports (VB .NET) directives for the corresponding namespaces (given in parenthesis below if different from the assembly name):

• ESRI.ArcGIS.Geodatabase

Development licensing	Deployment licensing
ArcGIS for Desktop Advanced	ArcGIS for Desktop Advanced
ArcGIS for Desktop Standard	ArcGIS for Desktop Standard
ArcGIS for Desktop Basic	ArcGIS for Desktop Basic
Engine Developer Kit	Engine: Geodatabase Update