Ado.net session07

Developing Database Applications Using ADO.NET and XML
Objectives

In this session, you will learn to:
Working in a disconnected environment

Ver. 1.0 Session 7 Slide 1 of 23

Working with Datasets and Datatables

In a disconnected environment, data is stored in datasets
and manipulations are performed in the datasets.
After the data has been manipulated in the dataset, the
changes are updated to the database.
A dataset is a disconnected, cached set of records that are
retrieved from a database.
The dataset acts like a virtual database containing tables,
rows, and columns.
The two main types of datasets are:
Typed dataset
Untyped dataset
Let us discuss each of these types in detail.


Working with Datasets and Datatables (Contd.)

Typed Dataset:
 A typed dataset is derived from the DataSet class and has an
associated XML schema, which is created at the time of
creation of the dataset.
 The XML schema contains information about the dataset
structure such as the tables, columns, and rows.
 The XML Schema Definition (XSD) language is used to define
the elements and attributes of XML documents.
 The structure of a typed dataset is decided at the time of its
creation.
 When a typed dataset is created, the data commands are
generated automatically by using the column names from the
data source.



Untyped Dataset:
An untyped dataset does not have any associated XML
schema.
In an untyped dataset, the tables and columns are represented
as collections.
Because an XML schema is not created for an untyped
dataset, the structure of an untyped dataset is not known
during compilation.
Untyped datasets find their use in cases where the structure of
the schema is not decided during compilation or the data being
used does not have a definite structure.



A dataset has its own object model, as shown in the
following figure.



• A dataset is created with the help of a DataSet object.
• The DataSet object is present in a DataSet class and is
defined in the System.Data namespace.
• The DataSet object contains a collection of DataTable
objects, each containing one or more tables.
• A DataTable object contains one or more columns, each
represented by a DataColumn object.
• To add a column to a DataTable, create a DataColumn
object and call the Add() method on the Columns
collection, which enables you to access the columns in a
datatable.



The following list describes some parameters that can be
specified for a column:
The name of the column
The data type of the column
Whether the column is read only
Whether the column permits null values
Whether the value of the column must be different in each row
Whether the column is an auto-increment column
Whether the column is an expression column



• Consider the following code snippet used for adding
columns in a DataTable:
DataSet ds = new DataSet(); Creating a DataSet
object
DataTable dt = ds.Tables.Add(); Creating a DataTable
object
dt.Columns.Add(“Store Id”, typeof(string)); Adding columns in a
DataTable
dt.Columns.Add(“Store Name”, typeof(string));
dt.Columns.Add(“Address”, typeof(string));



• A DataTable object also has a Rows collection that allows
rows to be accessed in a dataset.
• The various methods performed on a row by using the
DataRow object are:
Add() Appends the row to the end of the table

InsertAt() Inserts the row at a specified position

Find() Accesses a row in a table by its primary key value

Select() Finds rows that match a specified condition
Remove() Removes the specified DataRow object

RemoveAt() Removes the row at a specified position
Delete() Removes a row provisionally from a table


Just a minute

Which method of the DataRow object accesses a row in a
table by its primary key value?
1. Find()
2. Select()
3. InsertAt()
4. Add()

Answer:
1. Find()



• In ADO.NET, you can navigate through multiple tables to
validate and summarize the data by using the
DataRelation object.
• By using primary key and foreign key constraints that use a
DataRelation object, you can create the relationship
between multiple tables.
• The primary key is a unique index and ensures the
uniqueness of data stored in that table for that particular
row.
• The foreign key is a constraint on a table that can reference
one or more columns in that table.
• The table that has a primary key constraint is known as the
Parent table, and the table that has a foreign key constraint
is known as the Child table.



A DataSet.Relations property gets the collection of
relations that link tables and allow navigation from Parent
tables to Child tables.
The Rule enumeration indicates the action that occurs
when a foreign key constraint is enforced.
The various Rule enumeration values are:
Cascade Deletes or updates the child DataRow object when the parent
DataRow object is deleted or its unique key is changed

None Throws an exception if the parent DataRow object is deleted or
its unique key is changed

SetDefault Sets the foreign key column(s) value to the default value of the
DataColumn object(s), if the parent DataRow object is deleted
or its unique key is changed
Sets the foreign key column(s) value to DbNull, if the parent
SetNull
DataRow object is deleted or its unique key is changed



• Sometimes, the data available in one DataSet can be
merged with another DataSet. Or, a copy of the
DataTable objects can be created so that the user can edit
or modify data, which can then be merged back to the
original dataset.
• The Merge() method is used to combine data from multiple
DataSet, DataTable, and DataRow objects.
• During merging of data within datasets, the
MissingSchemaAction enumeration specifies the action
to be taken when the data added to the dataset and the
required DataTable or DataColumn is missing.



The various values of MissingSchemaAction
enumeration are:
Add Adds the DataTable and DataColumn
objects to complete the schema

AddWithPrimaryKey Adds the DataTable, DataColumn,
and PrimaryKey objects to complete
the schema
Error Throws an exception if the DataColumn
does not exist in the DataSet that is
being updated
Ignore Ignores data that resides in
DataColumns that are not in the
DataSet being updated


Working with Dataviews

• A dataview provides a dynamic view of data stored in a
datatable.
• If any data is modified in the datatable, the dataview
associated with the datatable will also show the modified
data.
Let us understand the object model of a dataview.


Working with Dataviews (Contd.)

The following figure shows the object model of a dataview.

DataSet Object

DataTable Object
DataView Object
DefaultView
Default Sort/Filter
Criteria

DataView Objects
Additional Views

Alternative
Sort/Filter Criteria



• A DataView object creates a fixed customized view of a
given DataTable object.
• You can create a DataView object to display the data
based on a criterion and another DataView object to
display the data based on a different criterion.
• The following figure shows how customized data is
displayed through dataviews.
Filter3

Filter2

Filter1

DataView1
Windows DataTable
Application DataView2

DataView3



• A dataview provides a sorted or filtered view of data in a
datatable.
• Sorting in a DataTable by using a DataView object is
done by using the Sort property.
• Filtering a DataTable by using the DataView object is
done by using the RowFilter and RowStateFilter
properties.


Just a minute

Which property of the DataView object returns a subset of
rows on the basis of the column values?
1. FindRows
2. RowFilter
3. RowStateFilter
4. Find

Answer:
2. RowFilter


Demo: Manipulating Data in a Disconnected Environment

Problem Statement:
Jane, a member of the HR team at Tebisco, needs to store the
details of employees who have recently joined the
organization. You need to create an application for Jane that
will enable her to add and save the details of new employees,
and if required, delete records of employees who are no longer
working in the organization. The employee code should get
automatically generated based on the format in the table. The
employee details will be stored in the empdetails table of the
HR database.


Summary

In this session, you learned that:
 A dataset, which is a part of disconnected environment, is a
disconnected, cached set of records that are retrieved from a
database.
 The two main types of datasets are:
 Typed datasets
 Untyped datasets
A typed dataset is derived from the DataSet class and has an
associated XML schema, which is created at the time of
creation of a dataset.
An untyped dataset does not have any associated XML
schema. As a result, the structure of an untyped dataset is not
known during compilation.


Summary (Contd.)

 The DataSet object contains a collection of DataTable
objects, each containing one or more tables.
 A DataTable object contains one or more columns, each
represented by a DataColumn object.
 A DataTable object also has a Rows collection, which allows
rows to be accessed in a dataset. A DataTable object
contains one or more rows, each represented by a DataRow
object.
 The DataRelation object is used to navigate through
multiple tables to validate and summarize the data.
 The primary key and foreign key constraints in a
DataRelation object create the relationship between the
tables in a schema.


Summary (Contd.)

 The Merge() method is used to combine data from multiple
DataSet, DataTable, and DataRow objects.
 A dataview, which is a part of the disconnected environment,
enables you to create a dynamic view of data stored in a
datatable.
 A DataTable can have multiple DataView objects assigned
to it, allowing the data to be viewed in different ways without
having to re-read from the database.
 Sorting in a DataTable by using the DataView object is done
by using the Sort property.
 Filtering in DataTable using DataView object is done by
using the RowFilter and RowStateFilter properties.


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