Tài liệu Enforcing Business Rules with Column Expressions docx

[ Team LiB ]Recipe 6.7 Enforcing Business Rules with Column Expressions Problem You need to enforce a business rule based on multiple columns in a table at the user interface tier.. Th

[ Team LiB ]

Recipe 6.7 Enforcing Business Rules with Column Expressions

Problem

You need to enforce a business rule based on multiple columns in a table at the user

interface tier

Solution

Use expression-based columns to enforce business rules at the user interface tier The

business rule for this solution is that the sum of Field1 and Field2 for a row in the table

must be 10

The schema of table TBL0607 used in this solution is shown in Table 6-5

Table 6-5 TBL0607 schema

The sample uses four stored procedures, which are shown in Example 6-21 through

Example 6-24:

SP0607_Delete

Used to delete a record from the table TBL0607 for a specified Id

SP0607_Get

Used to retrieve a record for a specified Id or all records from the table TBL0607 SP0607_Insert

Used to insert a record into the table TBL0607

SP0607_Update

Used to update a record in the table TBL0607

Example 6-21 Stored procedure: SP0607_Delete

CREATE PROCEDURE SP0607_Delete

@Id int

AS

SET NOCOUNT ON

delete

from

TBL0607

where

Id=@Id

return 0

Example 6-22 Stored procedure: SP0607_Get

CREATE PROCEDURE SP0607_Get

@Id int=null

AS

SET NOCOUNT ON

if @Id is not null

begin

select

Id,

Field1,

Field2

from

TBL0607

where

Id=@Id

return 0

end

select

Id,

Field1,

Field2

from

TBL0607

return 0

Example 6-23 Stored procedure: SP0607_Insert

CREATE PROCEDURE SP0607_Insert

@Id int,

@Field1 int,

@Field2 int

AS

SET NOCOUNT ON

insert TBL0607(

Id,

Field1,

Field2)

values (

@Id,

@Field1,

@Field2)

if @@rowcount=0

return 1

return 0

Example 6-24 Stored procedure: SP0607_Update

CREATE PROCEDURE SP0607_Update

@Id int,

@Field1 int,

@Field2 int

AS

SET NOCOUNT ON

update

TBL0607

set

Field1=@Field1,

Field2=@Field2

where

Id=@Id

if @@rowcount=0

return 1

return 0

The sample code contains three event handlers:

Form.Load

Sets up the sample by creating a DataTable and creating a schema for it matching TBL0607 in the database An expression column is added to the table The

calculation returns a Boolean value indicating whether the sum of Field1 and Field2 is equal to 10 A DataAdapter is created and event handler is attached to handle its RowUpdating event Delete, insert, and update commands using the stored procedures in this solution are created for the DataAdapter The

DataAdapter is used to fill the table and its default view is bound to the data grid

on the form

DataAdapter.RowUpdating

Checks whether a row is being updated or inserted and whether the value of the expression column is false indicating that the data is invalid according to the business rule defined by the expression in the column If the business rule has not been met, an error is set on the row and the update for the row is skipped

Update Button.Click

Uses the DataAdapter to update changes made to the DataTable back to table TBL0607 in the database

The C# code is shown in Example 6-25

Example 6-25 File: EnforceBusinessRulesWithColumnExpressionsForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Windows.Forms;

using System.Data;

using System.Data.SqlClient;

private DataTable dt;

private SqlDataAdapter da;

private const String TABLENAME = "TBL0607";

// Table column name constants

private const String ID_FIELD = "Id";

private const String FIELD1_FIELD = "Field1";

private const String FIELD2_FIELD = "Field2";

private const String CONSTRAINT_EXPRESSION = "ConstraintExpression";

// Stored procedure name constants

private const String DELETE_SP = "SP0607_Delete";

private const String GET_SP = "SP0607_Get";

private const String INSERT_SP = "SP0607_Insert";

private const String UPDATE_SP = "SP0607_Update";

// Stored procedure parameter name constants for table

private const String ID_PARM = "@Id";

private const String FIELD1_PARM = "@Field1";

private const String FIELD2_PARM = "@Field2";

//

private void EnforceBusinessRulesWithColumnExpressionsForm_Load(

object sender, System.EventArgs e)

{

DataColumnCollection cols;

// Build the table

dt = new DataTable(TABLENAME);

cols = dt.Columns;

cols.Add(ID_FIELD, typeof(Int32));

cols.Add(FIELD1_FIELD, typeof(Int32));

cols.Add(FIELD2_FIELD, typeof(Int32));

// add the primary key

dt.PrimaryKey = new DataColumn[] {cols[ID_FIELD]};

// Expression to evaluate whether the sum of Field1 and Field2

// equals 10

cols.Add(CONSTRAINT_EXPRESSION, typeof(Boolean), FIELD1_FIELD + "+" + FIELD2_FIELD + " = 10");

// Create the DataAdapter, handling the RowUpdating event

da = new SqlDataAdapter( );

da.RowUpdating += new SqlRowUpdatingEventHandler(da_RowUpdating); SqlConnection conn = new SqlConnection(

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

// Build the select command

SqlCommand selectCommand = new SqlCommand(GET_SP, conn);

selectCommand.CommandType = CommandType.StoredProcedure;

da.SelectCommand = selectCommand;

// Build the delete command

SqlCommand deleteCommand = new SqlCommand(DELETE_SP, conn); deleteCommand.CommandType = CommandType.StoredProcedure;

deleteCommand.Parameters.Add(ID_PARM, SqlDbType.Int, 0, ID_FIELD); da.DeleteCommand = deleteCommand;

// Build the insert command

SqlCommand insertCommand = new SqlCommand(INSERT_SP, conn); insertCommand.CommandType = CommandType.StoredProcedure;

insertCommand.Parameters.Add(ID_PARM, SqlDbType.Int, 0, ID_FIELD); insertCommand.Parameters.Add(FIELD1_PARM, SqlDbType.Int, 0,

FIELD1_FIELD);

insertCommand.Parameters.Add(FIELD2_PARM, SqlDbType.Int, 0,

FIELD2_FIELD);

da.InsertCommand = insertCommand;

// Build the update command

SqlCommand updateCommand = new SqlCommand(UPDATE_SP, conn); updateCommand.CommandType = CommandType.StoredProcedure;

updateCommand.Parameters.Add(ID_PARM, SqlDbType.Int, 0, ID_FIELD); updateCommand.Parameters.Add(FIELD1_PARM, SqlDbType.Int, 0,

FIELD1_FIELD);

updateCommand.Parameters.Add(FIELD2_PARM, SqlDbType.Int, 0,

FIELD2_FIELD);

da.UpdateCommand = updateCommand;

// Fill the table

da.Fill(dt);

// Bind the default view of the table to the grid

dataGrid.DataSource = dt.DefaultView;

}

private void da_RowUpdating(object sender, SqlRowUpdatingEventArgs e)

{

// For insert or update statements, check that the

// calculated constraint column is true

if((e.StatementType == StatementType.Insert ||

e.StatementType == StatementType.Update) &&

!(bool)e.Row[CONSTRAINT_EXPRESSION])

{

// Constraint has not been met

// Set an error on the row and skip it

e.Row.RowError = "Constraint error.";

e.Status = UpdateStatus.SkipCurrentRow;

}

}

private void updateButton_Click(object sender, System.EventArgs e)

{

try

{

da.Update(dt);

}

catch(Exception ex)

{

MessageBox.Show(ex.Message);

}

}

Discussion

The RowUpdating event of the DataAdapter occurs during the Update( ) method before the command to update a row is executed against the data source The event fires with

each row update attempt

The RowUpdating event handler receives an argument of type RowUpdatingEventArgs that provides information specifically related to the event as described in Table 6-6

Table 6-6 RowUpdatingEventArgs properties Property Description

Command Gets the Command to execute during the Update( ) method

Errors Gets errors generated by the NET data provider when the Command

was executed

Row Gets the DataRow to send through the Update( ) method

StatementType

Gets the type of SQL statement to execute This is one of the following values from the StatementType enumeration: Select, Insert, Update, or Delete

Status

Gets or sets the action to take with the current and remaining rows during the Update( ) method This is a value from the UpdateStatus enumeration (described in Table 6-7)

TableMapping Gets the DataTableMapping to send through the Update( ) method

Table 6-7 describes the values in the UpdateStatus enumeration used by the Status

property of the RowUpdatingEventArgs object

Table 6-7 UpdateStatus enumeration Value Description

Continue Continue processing the rows This is the default value

ErrorsOccurred The event handler reports that the update should be treated as

an error

SkipAllRemainingRows Do not update the current row and skip updating the

remaining rows

SkipCurrentRow Do not update the current row and continue updating with the

subsequent row

The Update( ) method of the DataAdapter raises two events for every row in the data

source that is updated The order of the events is:

1 The values in the DataRow are moved to parameter values

2 The OnRowUpdating event is raised

3 The update command executes against the row in the data source

4 If the UpdatedRowSource property of the Command is set to FirstReturnedRecord

or Both, the first returned result is placed in the DataRow

5 If the UpdateRowSource property of the Command is set to OutputParameters or

Both, the output parameters are placed in the DataRow

6 The OnDataRowUpdated event is raised

7 AcceptChanges( ) is called

If zero rows are affected, the DBConcurrencyException is raised during the update

operation on a row This usually indicates a concurrency violation

The solution uses the RowUpdating event of the DataAdapter to check whether the expression column in the DataTable is true, indicating that the business rule has been satisfied, before a database record is updated If the expression if false, an error is set on the row and the Status is set to SkipCurrentRow preventing the record in the database from being updated and continuing the processing with the next row

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