Tài liệu Merging Data pptx

The sample code contains four event handlers and a single method: Form.Load Sets up the sample by creating two DataSet objects each with a single DataTable containing different subset of

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Recipe 5.6 Merging Data

Problem

You have two DataSet objects with the same schema, but containing different data You need to combine data from these two DataSet objects without creating duplicate rows

Solution

Use the DataSet.Merge( ) method with the appropriate MissingSchemaAction

enumeration values

The sample code contains four event handlers and a single method:

Form.Load

Sets up the sample by creating two DataSet objects each with a single DataTable containing different subset of data from the Employees table in Northwind The default view for each table is bound to a data grid on the form

MergeA Button.Click

The first Button.Click calls the Merge( ) method to merge the first DataSet into the second

MergeB Button.Click

A second Button.Click calls the Merge( ) method to merge the second DataSet into the first

Clear Button.Click

A third Button.Click clears the data grid displaying the results of either merge Merge( )

This method takes two DataTable arguments The first DataTable is copied to a new DataTable and the second DataTable is merged into it with the specified MissingSchemaAction The default view of the result DataTable is bound to a data grid on the form

The C# code is shown in Example 5-6

Example 5-6 File: MergingDataForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Windows.Forms;

using System.Data;

using System.Data.SqlClient;

private SqlDataAdapter daA, daB;

private DataSet dsA, dsB;

//

private void MergingDataForm_Load(object sender, System.EventArgs e) {

// Fill the schema and data for table A

String sqlText = "SELECT EmployeeID, LastName, FirstName, Title " + "FROM Employees WHERE EmployeeID BETWEEN 1 AND 5"; // Set up the DataAdapter and CommandBuilder for table A

SqlCommandBuilder cbA = new SqlCommandBuilder(daA);

daA = new SqlDataAdapter(sqlText,

ConfigurationSettings.AppSettings["Sql_SqlAuth_ConnectString"]); // Define DataSet A and fill its table A with schema and data

dsA = new DataSet("A");

daA.FillSchema(dsA, SchemaType.Source, "Employees");

daA.Fill(dsA, "Employees");

// Bind the default view for table A to the grid

dataGridA.DataSource = dsA.Tables["Employees"].DefaultView;

// Fill the schema and data for table B

sqlText = "SELECT EmployeeID, LastName, FirstName, " +

"BirthDate, HireDate " +

"FROM Employees WHERE EmployeeID BETWEEN 4 AND 8"; // Set up the DataAdapter and CommandBuilder for table B

daB = new SqlDataAdapter(sqlText,

ConfigurationSettings.AppSettings["Sql_SqlAuth_ConnectString"]); SqlCommandBuilder cbB = new SqlCommandBuilder(daB);

// Define DataSet B and fill its table B with schema and data

dsB = new DataSet("B");

daB.FillSchema(dsB, SchemaType.Source, "Employees");

daB.Fill(dsB, "Employees");

// Bind the default view for table B to the grid

dataGridB.DataSource = dsB.Tables["Employees"].DefaultView;

}

private void Merge(DataTable dtSource, DataTable dtDest)

{

// Set the missing schema value to the default and read

// actual value, if otherwise, from the radio buttons

MissingSchemaAction msa = MissingSchemaAction.Add;

if(addWithKeyRadioButton.Checked)

msa = MissingSchemaAction.AddWithKey;

else if(errorRadioButton.Checked)

msa = MissingSchemaAction.Error;

else if(ignoreRadioButton.Checked)

msa = MissingSchemaAction.Ignore;

// Create the merge DataSet and copy table B into it

DataSet ds = new DataSet("Merge");

ds.Tables.Add(dtDest.Copy( ));

try

{

// Merge table A into the DataSet

ds.Merge(dtSource, false, msa);

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

// Bind the merge result table default view to the grid

dataGridMerge.DataSource = ds.Tables[0].DefaultView;

dataGridMerge.CaptionText = "Merge Results: " +

dtSource.DataSet.DataSetName + " into " +

dtDest.DataSet.DataSetName;

}

private void mergeAIntoBButton_Click(object sender, System.EventArgs e) {

Merge(dsA.Tables["Employees"], dsB.Tables["Employees"]);

}

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

{

Merge(dsB.Tables["Employees"], dsA.Tables["Employees"]);

}

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

{

dataGridMerge.DataSource = null;

dataGridMerge.CaptionText = "";

}

Discussion

The Merge( ) method of the DataSet can merge a DataRow array, a DataTable, or a DataSet into an existing DataSet If the existing DataSet has a primary key defined, the incoming data is matched to rows having the same primary key values Where matches are found, the existing row is updated with the new values Otherwise, rows are appended

to the existing table

There are two arguments that can be optionally specified in the overloaded Merge( ) methods

The first, preserveChanges, is a Boolean value that indicates whether incoming values will overwrite changes made to the existing DataSet If preserveChanges is false, the default, both the Current and Original row are overwritten with incoming values and the RowState of the row is set to the RowState of the incoming row Exceptions are shown in Table 5-2

Table 5-2 Exceptions to PreserveChanges argument when PreserveChanges =

false

Incoming

RowState

Existing

Unchanged Modified,

Deleted, or Added Modified Added

Unchanged, Modified, or Deleted

Modified Also, data in the Original version of the existing row is not overwritten because the Original version of the incoming row does not exist

If preserveChanges is specified as true, the values in the Current version of the existing row are maintained while values in the Original version of the existing row are

overwritten with the Original values for the incoming row The RowState of the existing row is set to Modified Exceptions are shown in Table 5-3

Table 5-3 Exceptions to PreserveChanges argument when PreserveChanges = true Incoming

RowState

Existing

Added Any

Modified Data in the Original version of the row is not overwritten because the Original version of the incoming row does not exist

The second argument is the missingSchemaAction argument, which accepts a value from the MissingSchemaAction enumeration that specifies how the Merge( ) method will

handle schema elements in the incoming data that are not part of the existing DataSet

Table 5-4 describes the values in the MissingSchemaAction enumeration

Table 5-4 MissingSchemaAction enumeration Value Decription

Add Add the new schema information and populate the new schema with

incoming values This is the default value

AddWithKey Add the new schema and primary key information and populate the new

schema with incoming values

Error Throw an exception if the incoming schema does not match the schema

of the existing DataSet

Ignore Ignore new schema information

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