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DotNet ADO.Net
What is the namespace in which .NET has the data functionality classes?
Following are the namespaces provided by .NET for data management :

System.data
This contains the basic objects used for accessing and storing relational data, such as DataSet, DataTable, and DataRelation. Each of these is independent of the type of data source and the way we connect to it.

System.Data.Oledb
It contains the objects that we use to connect to a data source via an OLE-DB provider, such as OledbConnection, OledbCommand, etc. These objects inherit from the common base classes, and so have the same properties, methods, and events as the SqlClient equivalents.

System.Data.SqlClient
This contains the objects that we use to connect to a data source via the Tabular Data Stream (TDS) interface of Microsoft SQL Server (only). This can generally provide better performance as it removes some of the intermediate layers required by an OLE-DB connection.

System.XML
This contains the basic objects required to create, read, store, write, and manipulate XML documents according to W3C recommendations.
Can you give a overview of ADO.NET architecture?
The most important section in ADO.NET architecture is "Data Provider". Data Provider provides access to datasource (SQL SERVER, ACCESS, ORACLE). In short it provides object to achieve functionalities like opening and closing connection, retrieve data and update data. The four main sections of a data provider :

Connection
Command object (This is the responsible object to use stored procedures)
Data Adapter (This object acts as a bridge between datastore and dataset)
Datareader (This object reads data from data store in forward only mode)
Dataset object represents disconnected and cached data. Dataset can have one or more Datatable and relations.
"DataView" object is used to sort and filter data in DataTable.
What are the two fundamental objects in ADO.NET?
Datareader and Dataset are the two fundamental objects in ADO.NET.
What is difference between dataset and datareader?
Following are some major differences between dataset and datareader :

Datareader provides forward-only and read-only access to data, while the Dataset object can hold more than one table from the same data source as well as the relationships between them.
Dataset is a disconnected architecture while datareader is connected architecture.
Dataset can persist contents while datareader can not persist contents, they are forward only.
What are major difference between classic ADO and ADO.NET?
Following are some major differences between both

As in classic ADO we had client and server side cursors they are no more present in ADO.NET. Note it is a disconnected model so they are no more applicable.
Locking is not supported dur to disconnected model
All data persist in XML as compared to classic ADO where data persisted in Binary format also.
What is the use of connection object?
They are used to connect a data to a Command object.

An OledbConnection object is used with an OLE-DB provider
A SqlConnection object uses Tabular Data Services (TDS) with MS SQL Server
What is the use of command objects?
They are used to connect connection object to Datareader or dataset. Following are the methods provided by command object :

ExecuteNonQuery : Executes the command defined in the CommandText property against the connection defined in the Connection property for a query that does not return any row. Returns an Integer indicating the number of rows affected by the query.

ExecuteReader : Executes the command defined in the CommandText property against the connection defined in the Connection property. Returns a "reader" object that is connected to the resulting rowset within the database,allowing the rows to be retrieved.

ExecuteScalar : Executes the command defined in the CommandText property against the connection defined in the Connection property. Returns only single value any other returned columns and rows are discarded. It is fast and efficient when only a "singleton" value is required.
What is the use of dataadapter?
These are objects that connect one or more Command objects to a Dataset object. They provide logic that would get data from the data store and populates the tables in the Dataset, or pushes the changes in the Dataset back into the data store.

An OleDbDataAdapter object is used with an OLE-DB provider.
A SqlDataAdapter object uses Tabular Data Services with MS SQL Server.
What are basic methods of Dataadapter?
There are three most commonly used methods of Dataadapter :

Fill : Executes the SelectCommand to fill the DataSet object with data from the data source. It is also be used to update an existing table in a DataSet with changes made to the data in the original datasource if there is a primary key in the table in the DataSet.

FillSchema : Uses the SelectCommand to extract just the schema for a table from the data source, and creates an empty table in the DataSet object with all the corresponding constraints.

Update : Calls the respective InsertCommand, UpdateCommand or DeleteCommand for each inserted, updated, or deleted row in the DataSet so as to update the original data source with the changes made to the content of the DataSet. This is a little like the UpdateBatch method provided by the ADO Recordset object, but in the DataSet it can be used to update more than one table.
What is Dataset object?
The DataSet provides the basis for disconnected storage and manipulation of relational data. We fill it from a data store, work with it while disconnected from the data store, then reconnect and flush changes back to the data store if required.
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