Tài liệu Creating DataSet Relationships from SQL Server Relationships docx

[ Team LiB ]Recipe 10.11 Creating DataSet Relationships from SQL Server Relationships Problem You need to create relationships between DataTable objects within your DataSet at runtime

[ Team LiB ]

Recipe 10.11 Creating DataSet Relationships from SQL Server Relationships

Problem

You need to create relationships between DataTable objects within your DataSet at

runtime based on the relationships that are defined in your SQL Server database

Solution

Use INFORMATION_SCHEMA views and system tables to create relationships

automatically at runtime

The schema of table TBL1011a used in this solution is shown in Table 10-5

Table 10-5 TBL1011a schema

The schema of table TBL1011b used in this solution is shown in Table 10-6

Table 10-6 TBL1011b schema

The sample code creates a DataSet containing the Orders table and Order Details table

from the Northwind sample database The tables TBL1011a and TBL1011b—related

through a multicolumn key—are also added to the DataSet Next, the result set of a query

of the INFORMATION_SCHEMA views are examined to determine the relationships

specified in the data source between the tables in the DataSet DataRelation objects are

created in the DataSet for the identified relationships

The C# code is shown in Example 10-11

Example 10-11 File: AutoDataRelationForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Collections;

using System.Text;

using System.Data;

using System.Data.SqlClient;

//

DataSet ds = new DataSet( );

SqlDataAdapter da;

// Add the Orders and Order Details tables to the DataSet

da = new SqlDataAdapter("SELECT * FROM Orders",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(ds, ORDERS_TABLE);

da = new SqlDataAdapter("SELECT * FROM [Order Details]",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(ds, ORDERDETAILS_TABLE);

// Add the TBL1011a and TBL1101b tables to the DataSet

da = new SqlDataAdapter("SELECT * FROM TBL1011a",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(ds, PARENTMULTICOLKEYTABLE);

da = new SqlDataAdapter("SELECT * FROM TBL1011b",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(ds, CHILDMULTICOLKEYTABLE);

StringBuilder result = new StringBuilder( );

String sqlText = "SELECT rc.CONSTRAINT_NAME, rc.UPDATE_RULE, " +

"rc.DELETE_RULE, " +

"kcuP.TABLE_NAME ParentTable, kcuC.TABLE_NAME ChildTable, " +

"kcuP.COLUMN_NAME ParentColumn, kcuC.COLUMN_NAME ChildColumn " + "FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS rc " + "LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcuP ON " + "rc.UNIQUE_CONSTRAINT_NAME = kcuP.CONSTRAINT_NAME " +

"LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcuC ON " + "rc.CONSTRAINT_NAME = kcuC.CONSTRAINT_NAME AND " +

"kcuP.ORDINAL_POSITION = kcuC.ORDINAL_POSITION " +

"ORDER BY rc.CONSTRAINT_NAME, kcuP.ORDINAL_POSITION";

// Create the connection and command to retrieve constraint information

SqlConnection conn = new SqlConnection(

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

SqlCommand cmd = new SqlCommand(sqlText, conn);

// Fill the DataReader with constraint information

conn.Open( );

SqlDataReader reader = cmd.ExecuteReader( );

String prevConstraintName = "";

String constraintName = "";

String parentTableName = "";

String childTableName = "";

bool updateCascade = false;

bool deleteCascade = false;

String relationName = "";

// Arrays to store related columns from constraints in DataReader

ArrayList parentColsAL = new ArrayList( );

ArrayList childColsAL = new ArrayList( );

DataColumn[] parentCols;

DataColumn[] childCols;

DataRelation dr;

bool isRecord = false;

// Iterate over the constraint collection for the database

do

{

// Read the next record from the DataReader

isRecord = reader.Read( );

// Store the current constraint as the previous constraint name

// to handle multicolumn-based relations

prevConstraintName = constraintName;

// Get the current constraint name

constraintName = isRecord ? reader["CONSTRAINT_NAME"].ToString( ) : "";

// If the constraint name has changed and both tables exist,

// create a relation based on the previous constraint column(s)

if (prevConstraintName != "" &&

constraintName != prevConstraintName &&

ds.Tables.Contains(parentTableName) &&

ds.Tables.Contains(childTableName))

{

// Create the parent and child column arrays

parentCols = new DataColumn[parentColsAL.Count];

parentColsAL.CopyTo(parentCols);

childCols = new DataColumn[childColsAL.Count];

childColsAL.CopyTo(childCols);

// Create the relation name based on the constraint name

relationName = prevConstraintName.Replace("FK_","RELATION_");

// Create the relation and add it to the DataSet

dr = new DataRelation(relationName, parentCols, childCols,

true);

ds.Relations.Add(dr);

// Set the cascade update and delete rules

dr.ChildKeyConstraint.UpdateRule =

updateCascade ? Rule.Cascade : Rule.None;

dr.ChildKeyConstraint.DeleteRule =

deleteCascade ? Rule.Cascade : Rule.None;

// Clear the parent and child column arrays for the previous

// constraint

parentColsAL.Clear( );

childColsAL.Clear( );

result.Append("Added relationship " + relationName +

" to DataSet." + Environment.NewLine);

}

if (isRecord)

{

// Store the current parent and child table names

parentTableName = reader["ParentTable"].ToString( );

childTableName = reader["ChildTable"].ToString( );

// Store the cascade update and delete for the current

// constraint

updateCascade = (reader["UPDATE_RULE"].ToString( ) ==

"CASCADE");

deleteCascade = (reader["DELETE_RULE"].ToString( ) ==

"CASCADE");

// Add the parent and child column for the current constraint

// to the ArrayLists, if both parent and child are in DataSet

if (ds.Tables.Contains(parentTableName) &&

ds.Tables.Contains(childTableName))

{

parentColsAL.Add(ds.Tables[parentTableName].Columns[

reader["ParentColumn"].ToString( )]);

childColsAL.Add(ds.Tables[childTableName].Columns[

reader["ChildColumn"].ToString( )]);

}

}

} while(isRecord);

// Close the DataReader and connection

reader.Close( );

conn.Close( );

resultTextBox.Text = result.ToString( );

Discussion

There is no ADO.NET data provider method that automatically returns information about table relationships that are defined in a database To get the relation information,

information views in SQL Server must be queried

The information required to reconstruct relationships between tables requires a query that pulls together information from two different information views,

INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS and

INFORMATION_SCHEMA.KEY_COLUMN_USAGE, and requires two joins into the latter table to obtain required information for both unique and foreign key constraints The REFERENTIAL_CONSTRAINTS table contains a row for each foreign key

constraint in the database The KEY_COLUMN_USAGE table contains one row for each row constrained as a key in the database

The solution starts by loading a DataSet with two sets of tables These tables are the Orders and Order Details tables from Northwind and a pair of sample tables—TBL0011a and TBL0011b—which demonstrate retrieving relation information for tables related on

more than one column

Next, the query to retrieve the data relationship information is constructed The SQL

statement used is:

SELECT

rc.CONSTRAINT_NAME, rc.UPDATE_RULE, rc.DELETE_RULE,

kcuP.TABLE_NAME ParentTable, kcuC.TABLE_NAME ChildTable,

kcuP.COLUMN_NAME ParentColumn, kcuC.COLUMN_NAME ChildColumn

FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS rc

LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcuP ON

rc.UNIQUE_CONSTRAINT_NAME = kcuP.CONSTRAINT_NAME

LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcuC ON

rc.CONSTRAINT_NAME = kcuC.CONSTRAINT_NAME AND

kcuP.ORDINAL_POSITION = kcuC.ORDINAL_POSITION

ORDER BY rc.CONSTRAINT_NAME, kcuP.ORDINAL_POSITION

This statement retrieves the constraint information needed to create the relations in the

DataSet based on the schema information in the database Specifically, the columns

returned are shown in Table 10-7

Table 10-7 Relation query columns Column Description

CONSTRAINT_NAME Name of the constraint

ParentTable Name of the parent table in the relationship

ChildTable Name of the child table in the relationship

ParentColumn Name of the column in the parent table

ChildColumn Name of the column in the child table

For relationships that are based on more than one column, there will be more than one

row in the result set that must be combined to create the DataRelation object in the

DataSet Notice that the statement groups the results that are returned by the constraint

name, grouping all records related to a single relation The result set is ordered by the

ORDINAL_POSITION field that defines the order of the columns in the relation When

iterating over the query results, if both the parent and child names are contained in the

result set, a relationship has been identified and processing continues For those

relationships, the column names for the parent and child tables are loaded into arrays

allowing relations based on multiple columns to be created

Once all of the columns for a relation have been loaded (this is determined by a change in the constraint name and the names of the parent and child tables), the DataRelation is created in the DataSet based on the parent and child column names in the arrays The update and delete cascade rules are set for the relation Although not necessary, the

sample names the relation based on the name of the constraint without the FK_ prefix

Once the DataRelation is created, processing of the result set resumes to determine the remaining relations

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