Tài liệu Retrieving Database Schema Information from SQL Server pptx

[ Team LiB ]Recipe 10.2 Retrieving Database Schema Information from SQL Server Problem You need to retrieve database schema information from a SQL Server database.. Solution Retrieve

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Recipe 10.2 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

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

TABLE_CONSTRAINTS All table constraints

TABLE_PRIVILEGES Tables with a privilege granted to or by the

current user

VIEW_COLUMN_USAGE Columns used in a view definition

VIEW_TABLE_USAGE Tables used in a view

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

TABLE_CATALOG nvarchar(128) Database name

TABLE_SCHEMA nvarchar(128) Table owner

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

Check_Constraints Check constraints

Check_Constraints_By_Table Check constraints defined for a catalog

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

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

Sql_Languages Conformance levels, options, and dialects supported by

the SQL implementation processing data Statistics Statistics

Tables_Info Tables and views

Table_Constraints Table constraints

Table_Statistics Available statistics on tables

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

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