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Implementing assemblies

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Applies to: SQL Server

This article provides information about the following areas to help you implement and work with assemblies in the database:

  • Creating assemblies
  • Modifying assemblies
  • Dropping, disabling, and enabling assemblies
  • Managing assembly versions

Create assemblies

Assemblies are created in SQL Server by using the Transact-SQL CREATE ASSEMBLY statement, or in the SQL Server Management Studio by using the Assembly Assisted Editor. Additionally, deploying a SQL Server Project in Microsoft Visual Studio registers an assembly in the database that was specified for the project. For more information, see Deploying CLR Database Objects.

Modify assemblies

Assemblies are modified in SQL Server by using the Transact-SQL ALTER ASSEMBLY statement or in SQL Server Management Studio by using the Assembly Assisted Editor.

You can modify an assembly when you want to perform the following actions:

  • Change the implementation of the assembly by uploading a newer version of the binaries of the assembly. For more information, see Manage assembly versions later in this article.

  • Change the permission set of the assembly. For more information, see Designing assemblies.

  • Change the visibility of the assembly. Visible assemblies are available for referencing in SQL Server. Nonvisible assemblies aren't available, even if they're uploaded in the database. By default, assemblies uploaded to an instance of SQL Server are visible.

  • Add or drop a debug or source file associated with the assembly.

Drop, disable, and enable assemblies

Assemblies are dropped by using the Transact-SQL DROP ASSEMBLY statement or SQL Server Management Studio.

By default, all assemblies that are created in SQL Server are disabled from executing. You can use the clr enabled option of the sp_configure system stored procedure, to disable or enable the execution of all assemblies that are uploaded in SQL Server. Disabling assembly execution prevents common language runtime (CLR) functions, stored procedures, triggers, aggregates, and user-defined types from executing, and stops any that are currently executing. Disabling assembly execution doesn't disable the ability to create, alter, or drop assemblies. For more information, see Server configuration: clr enabled.

For more information, see sp_configure.

Manage assembly versions

When an assembly is uploaded to an instance SQL Server, the assembly is stored and managed within the database system catalogs. Any changes made to the definition of the assembly in the Microsoft .NET Framework should be propagated to the assembly that is stored in the database catalog.

When you have to modify an assembly, you must issue an ALTER ASSEMBLY statement to update the assembly in the database. This statement updates the assembly to the latest copy of .NET Framework modules holding its implementation.

The WITH UNCHECKED DATA clause of the ALTER ASSEMBLY statement instructs SQL Server to refresh even those assemblies upon which persisted data in the database is dependent. Specifically, you must specify WITH UNCHECKED DATA if any of the following exist:

  • Persisted computed columns that reference methods in the assembly, either directly, or indirectly, through Transact-SQL functions or methods.

  • Columns of a CLR user-defined type that depend on the assembly, and the type implements a UserDefined (non-Native) serialization format.

Caution

If WITH UNCHECKED DATA isn't specified, SQL Server tries to prevent ALTER ASSEMBLY from executing if the new assembly version affects existing data in tables, indexes, or other persistent sites. However, SQL Server doesn't guarantee that computed columns, indexes, indexed views, or expressions will be consistent with the underlying routines and types when the CLR assembly is updated. Be careful when you execute ALTER ASSEMBLY to make sure that there's no mismatch between the result of an expression and a value that is based on that expression stored in the assembly.

Only members of the db_owner and db_ddlowner fixed database role can execute run ALTER ASSEMBLY by using the WITH UNCHECKED DATA clause.

SQL Server posts a message to the Windows Application event log that the assembly was modified with unchecked data in the tables. SQL Server then marks any tables that contain data dependent on the assembly as having unchecked data. The has_unchecked_assembly_data column of the sys.tables catalog view contains the value 1 for tables that contain unchecked data, and 0 for tables without unchecked data.

To resolve the integrity of unchecked data, run DBCC CHECKDB WITH EXTENDED_LOGICAL_CHECKS against each table that has unchecked data. If DBCC CHECKDB WITH EXTENDED_LOGICAL_CHECKS fails, you must either delete the table rows that aren't valid or modify the assembly code to address problems, and then issue more ALTER ASSEMBLY statements.

ALTER ASSEMBLY changes the assembly version. The culture and public key token of the assembly remain the same. SQL Server doesn't allow registering different versions of an assembly with the same name, culture, and public key.

Interactions with computer-wide policy for version binding

If references to assemblies stored in SQL Server are redirected to specific versions by using publisher policy or computer-wide administrator policy, you must do either of the following actions:

  • Make sure the new version to which this redirection is made is in the database.

  • Modify any statements to the external policy files of the computer or publisher policy to make sure that they reference the specific version that is in the database.

Otherwise, an attempt to load a new assembly version to the instance of SQL Server fails.

For more information, see ALTER ASSEMBLY.

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