Tài liệu Building a DataSet Programmatically docx

[ Team LiB ]Recipe 2.2 Building a DataSet Programmatically Problem You want to build a DataSet programmatically—including adding tables, columns, primary keys, and relations—from a sch

[ Team LiB ]

Recipe 2.2 Building a DataSet Programmatically

Problem

You want to build a DataSet programmatically—including adding tables, columns,

primary keys, and relations—from a schema that you have designed

Solution

The following example shows how to build a complex DataSet programmatically,

including how to build and add tables, columns, primary key constraints, relations, and column mappings Use this as a template for building your own DataSet

The sample code creates a DataSet A DataTable object is created representing the Orders table in Northwind Columns are added, including the auto-increment primary key, to the table The table is added to the DataSet The process is repeated for a DataTable

representing the Order Details table in Northwind A DataRelation is created relating the two tables Finally, the tables are filled with data from Northwind

The C# code is shown in Example 2-2

Example 2-2 File: BuildDataSetProgramaticallyForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Data;

using System.Data.SqlClient;

//

// Create the DataSet

DataSet ds = new DataSet("MyDataSet");

// Build the Orders (parent) table

DataTable parentTable = new DataTable("Orders");

DataColumnCollection cols = parentTable.Columns;

// Add the identity field

DataColumn column = cols.Add("OrderID", typeof(System.Int32));

column.AutoIncrement = true;

column.AutoIncrementSeed = -1;

column.AutoIncrementStep = -1;

// Add the other fields

cols.Add("CustomerID", typeof(System.String)).MaxLength = 5; cols.Add("EmployeeID", typeof(System.Int32));

cols.Add("OrderDate", typeof(System.DateTime));

cols.Add("RequiredDate", typeof(System.DateTime));

cols.Add("ShippedDate", typeof(System.DateTime));

cols.Add("ShipVia", typeof(System.Int32));

cols.Add("Freight", typeof(System.Decimal));

cols.Add("ShipName", typeof(System.String)).MaxLength = 40; cols.Add("ShipAddress", typeof(System.String)).MaxLength = 60; cols.Add("ShipCity", typeof(System.String)).MaxLength = 15;

cols.Add("ShipRegion", typeof(System.String)).MaxLength = 15; cols.Add("ShipPostalCode", typeof(System.String)).MaxLength = 10; cols.Add("ShipCountry", typeof(System.String)).MaxLength = 15; // Set the primary key

parentTable.PrimaryKey = new DataColumn[] {cols["OrderID"]}; // Add the Orders table to the DataSet

ds.Tables.Add(parentTable);

// Build the Order Details (child) table

DataTable childTable = new DataTable("Order Details");

cols = childTable.Columns;

// Add the PK fields

cols.Add("OrderID", typeof(System.Int32)).AllowDBNull = false; cols.Add("ProductID", typeof(System.Int32)).AllowDBNull = false; // Add the other fields

cols.Add("UnitPrice", typeof(System.Decimal)).AllowDBNull = false; cols.Add("Quantity", typeof(System.Int16)).AllowDBNull = false; cols.Add("Discount", typeof(System.Single)).AllowDBNull = false; // Set the primary key

childTable.PrimaryKey = new DataColumn[]

{

cols["OrderID"],

cols["ProductID"]

};

// Add the Order Details table to the DataSet

ds.Tables.Add(childTable);

// Add the relationship between parent and child tables

ds.Relations.Add("Order_OrderDetails_Relation",

parentTable.Columns["OrderID"], childTable.Columns["OrderID"], true);

// Fill the tables from the data source

SqlDataAdapter da;

String sqlText;

sqlText = "SELECT OrderID, CustomerID, EmployeeID, OrderDate, " +

"RequiredDate, ShippedDate, ShipVia, Freight, ShipName, " +

"ShipAddress, ShipCity, ShipRegion, ShipPostalCode, ShipCountry " +

"FROM Orders";

da = new SqlDataAdapter(sqlText,

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(parentTable);

sqlText = "SELECT OrderID, ProductID, UnitPrice, Quantity, Discount " +

"FROM [Order Details]";

da = new SqlDataAdapter(sqlText,

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

da.Fill(childTable);

Discussion

The steps to build a complex DataSet programmatically, as shown in the code for the solution, are:

1 Design the DataSet identifying the tables, columns, indexes, constraints, and data relations that need to be created

2 Create a new DataSet, naming it in the constructor

3 Create a new DataTable, naming it in the constructor

4 Add a column to the ColumnCollection of the table using the Add( ) method exposed by the Columns property of the DataTable specifying the name and data type of the column If the column is a character-type column, define its maximum length If the column is an auto-increment column, set the AutoIncrement property

to true and set both the AutoIncrementSeed and AutoIncrementStep properties of the column to -1 (For more information about using auto-increment columns, see Recipe 4.1) Repeat step 4 for each column in the table

5 Define the primary key for the table by setting the PrimaryKey property of the DataTable to the array of primary key DataColumn objects

6 Add the new table to the DataSet using the Add( ) method of the

DataTableCollection exposed by the Tables property of the DataSet

7 Repeat steps 3-6 for each table in the DataSet

8 Create a data relationship between two related tables in the DataSet by using the Add( ) method of the DataRelationCollection exposed by the Relations property of

the DataSet Specify the relationship name, the related columns, and whether constraints are to be created when calling the Add( ) method Repeat step 8 for each data relationship in the DataSet

The steps continue, demonstrating how to fill the new DataSet:

9 To fill the DataSet with data from the data source, create a DataAdapter defining the SQL select statement and the connection string in the constructor

10 Use the Fill( ) method of the DataSet to fill the table Specify the table name to be filled in the second argument of the Fill( ) method

11 Repeat steps 9 and 10 for each table to be filled See Recipe 2.1 for information about how to fill related tables from the data source without raising constraint violation errors

[ Team LiB ]