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 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. [ 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. following syntax: INFORMATION _SCHEMA. TABLES Table 10-1 lists the information schema views available in SQL Server 2000. Table 10-1. Information schema views