object_id

Is the ID of the object to be used. object_id is int, and assumed to represent an object in the current database context.

nvarchar(max)

Returns NULL on error or if a caller does not have permission to view the object.

A user can only view the metadata of securables that the user owns or on which the user has been granted permission. This means that metadata-emitting, built-in functions such as OBJECT_DEFINITION may return NULL if the user does not have any permission on the object. For more information, see Metadata Visibility Configuration and Troubleshooting Metadata Visibility.

The SQL Server Database Engine assumes that object_id is in the current database context. The collation of the object definition always matches that of the calling database context.

OBJECT_DEFINITION applies to the following object types:

• C = Check constraint
  
• D = Default (constraint or stand-alone)
  
• P = SQL stored procedure
  
• FN = SQL scalar function
  
• R = Rule
  
• RF = Replication filter procedure
  
• TR = SQL trigger (schema-scoped DML trigger, or DDL trigger at either the database or server scope)
  
• IF = SQL inline table-valued function
  
• TF = SQL table-valued function
  
• V = View
  

System object definitions are publicly visible. The definition of user objects is visible to the object owner or grantees that have any one of the following permissions: ALTER, CONTROL, TAKE OWNERSHIP, or VIEW DEFINITION. These permissions are implicitly held by members of the db_owner, db_ddladmin, and db_securityadmin fixed database roles.

A. Returning the source text of a user-defined object

USE AdventureWorks;
GO
SELECT OBJECT_DEFINITION (OBJECT_ID(N'Person.uAddress')) AS [Trigger Definition]; 
GO

B. Returning the source text of a system object

USE AdventureWorks;
GO
SELECT OBJECT_DEFINITION (OBJECT_ID(N'sys.sp_columns')) AS [Object Definition];
GO

Reference

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