Retrieving Database Schema Information from SQL Server

Problem

You need to retrieve database schema information from a SQL Server database.

Solution

Retrieve table schema information using either information schema views or the OLE DB .NET data provider Connection object.

The sample code retrieves a list of tables in the Northwind sample database.

The C# code is shown in Example 10-2.

Example 10-2. File: DatabaseSchemaForm.cs

// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Data.OleDb;

// . . . 

DataTable schemaTable;

if(sqlServerRadioButton.Checked)
{
 String getSchemaTableText = "SELECT * " +
 "FROM INFORMATION_SCHEMA.TABLES " +
 "WHERE TABLE_TYPE = 'BASE TABLE' ORDER BY TABLE_TYPE";

 // Retrieve the schema table contents.
 SqlDataAdapter da = new SqlDataAdapter(getSchemaTableText,
 ConfigurationSettings.AppSettings["Sql_ConnectString"]);
 schemaTable = new DataTable( );
 da.Fill(schemaTable);

 schemaDataGrid.CaptionText = "SQL Server .NET Provider";
}
else
{
 OleDbConnection conn = new OleDbConnection(
 ConfigurationSettings.AppSettings["OleDb_ConnectString"]);
 conn.Open( );
 // Get the schema table.
 schemaTable = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables,
 new object[] {null, null, null, "TABLE"});
 conn.Close( );

 schemaDataGrid.CaptionText = "OLE DB .NET Provider";
}

// Bind the default view of schema table to the grid.
schemaDataGrid.DataSource = schemaTable.DefaultView;

Discussion

The first solution uses information schema views that are available in SQL Server 7.0 and later. These views provide system-table independent access to SQL Server metadata. Although based on the sysobjects and syscomments system tables, the views allow applications to continue to work properly even if the system tables change. They provide an alternative to the system stored procedures that were previously used and are still available. The INFORMATION_SCHEMA views conform to the SQL-92 Standard.

The views are defined within each database in a schema named INFORMATION_SCHEMA . To access them, specify the fully qualified view name . In the solution, the view for the tables is accessed through the following syntax:

INFORMATION_SCHEMA.TABLES

Table 10-1 lists the information schema views available in SQL Server 2000.

Table 10-1. Information schema views

Name

Description

CHECK CONSTRAINTS

CHECK constraints

COLUMN_DOMAIN_USAGE

Columns that have a user -defined data type

COLUMN_PRIVILEGES

Columns with a privilege granted to or by the current user

COLUMNS

All columns

CONSTRAINT_COLUMN_USAGE

Columns that have a constraint defined on them

CONSTRAINT_TABLE_USAGE

Tables that have a constraint defined on them

DOMAIN_CONSTRAINTS

User-defined data types with a rule bound to them

DOMAINS

All user-defined data types

KEY_COLUMN_USAGE

Columns constrained as a key

PARAMETERS

All parameters for user-defined functions and stored procedures

REFERENTIAL_CONSTRAINTS

All foreign constraints

ROUTINE_COLUMNS

Columns returned by table-valued functions

ROUTINES

All user-defined functions and stored procedures

SCHEMATA

All databases

TABLE_CONSTRAINTS

All table constraints

TABLE_PRIVILEGES

Tables with a privilege granted to or by the current user

TABLES

All tables

VIEW_COLUMN_USAGE

Columns used in a view definition

VIEW_TABLE_USAGE

Tables used in a view

VIEWS

All views

The metadata returned will be limited to that which the user has permission to view. Like any other views, information schema views can also be joined in queries or participate in complex queries to extract specific information. For detailed information about the different views available, refer to SQL Server Books Online.

The solution shows how to retrieve table metadata using the INFORMATION_SCHEMA.TABLES view. It returns data as shown in Table 10-2.

Table 10-2. INFORMATION_SCHEMA.TABLES metadata

Column name

Data type

Description

TABLE_CATALOG

nvarchar (128)

Database name

TABLE_SCHEMA

nvarchar (128)

Table owner

TABLE_NAME

sysname

Table name

TABLE_TYPE

varchar (10)

Table type (either BASE_TABLE or VIEW )

The TABLES view is queried for all columns where the table type is BASE_TABLE in order to return only information about tables and not views.

The second solution uses the GetOleDbSchemaTable( ) method of the OleDbConnection object. This method returns schema information from a database as indicated by a GUID enumerated in the OleDbSchemaGuid class and detailed in Table 10-3.

Table 10-3. OleDbSchemaGuid public fields

Field

Description

Assertions

Assertions

Catalogs

Physical attributes and assertions for catalogs accessible from the data source

Character_Sets

Character sets

Check_Constraints

Check constraints

Check_Constraints_By_Table

Check constraints defined for a catalog

Collations

Character collations

Columns

Columns in tables and view

Column_Domain_Usage

Columns that are dependant on a domain defined in the catalog

Column_Privileges

Privileges on columns

Constraint_Column_Usage

Columns used by referential constraints, unique constraints, check constraints, and assertions

Constraint_Table_Usage

Tables used by referential constraints, unique constraints, check constraints, and assertions

DbInfoLiterals

Provider-specific literals used in text commands

Foreign_Keys

Foreign key columns

Indexes

Indexes

Key_Column_Usage

Columns constrained as keys

Primary_Keys

Columns that comprise primary keys

Procedures

Procedures

Procedure_Columns

Columns of row sets returned by procedures

Procedure_Parameters

Parameters and return codes of procedures

Provider_Types

Base data types supported by the .NET data provider for OLE DB

Referential_Constraints

Referential constraints

Schemata

Schema objects

Sql_Languages

Conformance levels, options, and dialects supported by the SQL implementation processing data

Statistics

Statistics

Tables

Tables and views

Tables_Info

Tables and views

Table_Constraints

Table constraints

Table_Privileges

Table privileges

Table_Statistics

Available statistics on tables

Translations

Defined character translations

Trustee

Trustee defined in the data source

Usage_Privileges

USAGE privileges on objects

Views

Views

View_Column_Usage

Columns in views

View_Table_Usage

Tables in views

As for information schema views, the metadata returned is limited to that which the user has permission to view. In addition to taking the Guid schema argument, you can further restrict the results of the GetOleDbSchemaTable( ) through the second argument, which is an object array specifying column restrictions applied to the result columns in the order in which they are returned. In this example, the schema argument is Tables , which returns a four-column result set containing all tables and views in the database. The fourth column describes the table type; specifying TABLE as the fourth object in the restrictions object array limits the result set to user tables.

Connecting to Data

Retrieving and Managing Data

Searching and Analyzing Data

Adding and Modifying Data

Copying and Transferring Data

Maintaining Database Integrity

Binding Data to .NET User Interfaces

Working with XML

Optimizing .NET Data Access

Enumerating and Maintaining Database Objects

Appendix A. Converting from C# to VB Syntax



ADO. NET Cookbook
ADO.NET 3.5 Cookbook (Cookbooks (OReilly))
ISBN: 0596101406
EAN: 2147483647
Year: 2002
Pages: 222
Authors: Bill Hamilton

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