No discussion of the new CLR features would be complete without a description of the security issues associated with using .NET assemblies and the SQL Server CLR. Unlike T-SQL, which doesn't have any native facilities for referencing resources outside the database, .NET assemblies are fully capable of accessing both system and network resources. Therefore, securing them is an important aspect of their development. With SQL Server 2005, Microsoft has integrated the user-based SQL Server security model with the permissions-based CLR security model.
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Following the SQL Server security model, users are able to access only database objects—including those created from .NET assemblies—to which they have user rights. The CLR security model extends this by providing control over the types of system resources that can be accessed by .NET code running on the server. CLR security permissions are specified at the time the assembly is created by using the WITH PERMISSION_SET clause of the CREATE ASSEMBLY statement. Table 3-4 summarizes the options for CLR database security permissions that can be applied to SQL Server database objects.
Table 3-4: CLR Database Object Security Options
Using the SAFE permission restricts all external access. The EXTERNAL_ACCESS permission enables some external access of resources using managed APIs. SQL Server impersonates the caller in order to access external resources. You must have the new EXTERNAL_ACCESS permission in order to create objects with this permission set. The UNSAFE permission is basically an anything-goes type of permission. All system resources can be accessed, and calls to both managed and unmanaged code are allowed. Only system administrators can create objects with UNSAFE permissions.
In addition to using the CREATE ASSEMBLY statement, you can also set the CLR database object permission using the project properties as is shown in Figure 3-16.
Figure 3-16: Setting the CLR permission
To interactively set the CLR permission level, open the project properties by selecting the Project | Properties option from the Visual Studio 2005 menu. Then open the Database tab and click the Permission Level drop-down. The project must be redeployed before the changes will take place.
Managing CLR database objects
As shown in Table 3-5, SQL Server 2005 provides system views that enable you to see the different CLR objects that are being used in the database.
Table 3-5: System Views to Manage CLR Database Objects
The previous tip is from "Developing CLR database objects: 10 tips in 10 minutes," excerpted from Chapter 3 of the book "Microsoft SQL Server 2005: A Developer's Guide" written by Michael Otey and Denielle Otey, courtesy of McGraw-Hill Publishing.
Basic Transact-SQL Programming Constructs
Tip 1: CLR integration
Tip 2: CLR and SQL Server 2005
Tip 3: Creating CLR database objects
Tip 4: CLR stored procedures
Tip 5: User-Defined Functions
Tip 6: CLR triggers
Tip 7: User-Defined Types
Tip 8: CLR aggregates
Tip 9: Debugging CLR database objects
Tip 10: .NET database object security