ADO.NET

(B)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
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.

(B) 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.In the below figure you can see 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.If you see the diagram it is not in direct connection with the data store (SQL SERVER , ORACLE etc) rather it talks with Data adapter , who is responsible for filling the dataset.Dataset can have one or more Datatable and relations.

(B)What are the two fundamental objects in ADO.NET ?
Datareader and Dataset are the two fundamental objects in ADO.NET.

(B)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 (in other words more than one rowset) from the same data source as well as the relationships between them.
√ Dataset is a disconnected architecture while datareader is connected architecture.
√ Dataset can persists contents while datareader can not persist contents they are forward only.

(I)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's a disconnected model so they are no more applicable.
√ Locking is not supported due to disconnected model.
√ All data is persisted in XML as compared to classic ADO where data was persisted in Binary format also.

(B)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

(B)What is the use of command objects and what are the methods provided by the command object ?
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 rows (an UPDATE, DELETE or INSERT).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 a single value (effectively the first column of the first row of the resulting rowset). Any other returned columns and rows are discarded. Fast and efficient when only a "singleton" value is required

(B)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 that data store, then reconnect and flush changes back to the data store if required.

(B)What are the various objects in Dataset ?
Dataset has a collection of DataTable object within the Tables collection. Each DataTable object contains a collection of DataRow objects and a collection of DataColumn objects. There are also collections for the primary keys,constraints, and default values used in this table which is called as constraint collection, and the parent and child relationships between the tables.Finally, there is a DefaultView object for each table. This is used to create a DataView object based on the table, so that the data can be searched, filtered or otherwise manipulated while displaying the data.

(B) How can we force the connection object to close after my datareader is closed ?
Command method Executereader takes a parameter called as CommandBehavior where in we can specify saying close connection automatically after the Datareader is close. pobjDataReader = pobjCommand.ExecuteReader(CommandBehavior.CloseConnection)

(B) I want to force the datareader to return only schema of the datastore rather than data ?
pobjDataReader = pobjCommand.ExecuteReader(CommandBehavior.SchemaOnly)

(B) How can we fine tune the command object when we are expecting a single row or a single value ?
Again CommandBehaviour enumeration provides two values SingleResult and SingleRow. If you are expecting a single value then pass “CommandBehaviour.SingleResult” and the query is optimized accordingly , if you are expecting single row then pass “CommandBehaviour.SingleRow” and query is optimized according to single row.

(B) Which is the best place to store connectionstring in .NET projects ?
Config files are the best place to store connection strings. If it’s a web-based application “Web.config” file will be used and if it’s a windows application “App.config” files will be used.

(B) What are steps involved to fill a dataset ?
Twist :- How can we use dataadapter to fill a dataset ?
Private Sub LoadData()
     Dim strConnectionString As String
     strConnectionString = AppSettings.Item(“ConnectionString”)
     Dim objConn As New SqlConnection(strConnectionString)
     objConn.Open()
     Dim objCommand As New SqlCommand(“Select FirstName from
     Employees”)
     objCommand.Connection = objConn
     Dim objDataAdapter As New SqlDataAdapter()
     objDataAdapter.SelectCommand = objCommand
     Dim objDataSet As New DataSet
     objDataAdapter.Fill(objDataSet)
End Sub

(B)What are the various methods provided by the dataset object to generate XML?
Note:- XML is one of the most important leap between classic ADO and ADO.NET. So this question is normally asked more generally how can we convert any data to XML format.Best answer is convert in to dataset and use the below methods.
√ ReadXML: Read’s a XML document in to Dataset.
√ GetXML: This is function’s which return’s a string containing XML document.
√ WriteXML: This write’s a XML data to disk.

(B) How can we save all data from dataset ?
Dataset has “AcceptChanges” method which commits all the changes since last time “Acceptchanges” has been executed.

(B) How can we check that some changes have been made to dataset since it was loaded ?
Twist :- How can we cancel all changes done in dataset ? , How do we get values which are changed in a dataset ?
For tracking down changes Dataset has two methods which comes as rescue “GetChanges “and “HasChanges”.
GetChanges
Return’s dataset which are changed since it was loaded or since Acceptchanges was executed.
HasChanges
This property indicate’s has any change’s been made since the dataset was loaded or acceptchanges method was executed. If we want to revert or abandon all change’s since the dataset was loaded use “RejectChanges”.

(B) How can we add/remove row’s in “DataTable” object of “DataSet” ?
“Datatable” provides “NewRow” method to add new row to “DataTable”.”DataTable” has “DataRowCollection” object which has all rows in a “DataTable” object.Following are the methods provided by “DataRowCollection” object :-
Add: Add’s a new row in DataTable
Remove: Remove’s a “DataRow” object from “DataTable”
RemoveAt: Remove’s a “DataRow” object from “DataTable” depending on index position of the “DataTable”.

(B) What’s basic use of “DataView” ?
“DataView” represent’s a complete table or can be small section of row’s depending on some criteria. It’s best used for sorting and finding data with in “datatable”. Dataview has the following method’s :-
Find: Take’s a array of value’s and return’s the index of the row.
FindRow: This also takes array of values but returns a collection of “DataRow”. If we want to manipulate data of “DataTable” object create “DataView” (Using the “DefaultView” we can create “DataView” object) of the “DataTable” object. and use the following functionalities :-
AddNew
Add’s a new row to the “DataView” object.
Delete
Deletes the specified row from “DataView” object.

(B) What’s difference between “DataSet” and “DataReader” ?
Following are the major difference between “DataSet” and “DataReader” :-
√ “DataSet” is a disconnected architecture , while “DataReader” has live connection while reading data.So if we want to cache data and pass to a different tier “DataSet” forms the best choice and it has decent XML support. √ When application needs to access data from more than one table “DataSet” forms the best choice.
√ If we need to move back while reading record’s , “datareader” does not support this functionality.
√ But one of the biggest drawbacks of DataSet is speed. As “DataSet” carry considerable overhead because of relations, multiple tables etc speed is slower than “DataReader”. Always try to use “DataReader” whereever possible, as it’s meant specially for speed performance.

(B) How can we add relation’s between table in a DataSet ?
Dim objRelation As DataRelation
objRelation=New
DataRelation("CustomerAddresses", objDataSet.Tables("Customer").Columns("Custid")
,objDataSet.Tables("Addresses").Columns("Custid_fk"))
objDataSet.Relations.Add(objRelation)

Relation’s can be added between “DataTable” object’s using the “DataRelation” object.Above sample code is trying to build a relationship between “Customer” and “Addresses” “Datatable” using “CustomerAddresses” “DataRelation” object.

(B) What’s the use of CommandBuilder ?
CommandBuilder builds “Parameter” objects automatically.Below is a simple code which uses commandbuilder to load its parameter object’s.

Dim pobjCommandBuilder As New OleDbCommandBuilder(pobjDataAdapter)
pobjCommandBuilder.DeriveParameters(pobjCommand)

Be careful while using “DeriveParameters” method as it needs a extra trip to the Datastore which can be very inefficient.

(B) What’s difference between “Optimistic” and “Pessimistic” locking ?
In pessimistic locking when user wants to update data it locks the record and till then no one can update data.Other user’s can only view the data when there is pessimistic locking. In optimistic locking multiple user’s can open the same record for updating, thus increase maximum concurrency.Record is only locked when updating the record.This is the most preferred way of locking practically.Now a days browser based application are very common and having pessimistic locking is not a practical solution.

(A) How many way’s are there to implement locking in ADO.NET ?
Following are the ways to implement locking using ADO.NET :-

√ When we call “Update” method of DataAdapter it handles locking internally.If the DataSet values are mot matching with current data in Database it raises Concurrency exception error.We can easily trap this error using Try. Catch block and raise appropriate error message to the user.

√ Define a Datetime stamp field in the table.When actually you are firing the UPDATE SQL statements compare the current timestamp with one existing in the database.Below is a sample SQL which checks for timestamp before updating and any mismatch in timestamp it will not update the records.This is the best practice used by industries for locking.
Update table1 set field1=@test where LastTimeStamp=@CurrentTimeStamp

√ Check for original values stored in SQL SERVER and actual changed values.In stored procedure check before updating that the old data is same as the current.Example in the below shown SQL before updating field1 we check that is the old field1 value same.If not then some one else has updated and necessary action has to be taken.
Update table1 set field1=@test where field1 = @oldfield1value

Locking can be handled at ADO.NET side or at SQL SERVER side i.e. in stored procedures.for more details of how to implementing locking in SQL SERVER read “What are different locks in SQL SERVER ?” in SQL SERVER chapter.

(A)How can we perform transactions in .NET?
The most common sequence of steps that would be performed while developing a transactional application is as follows:
√ Open a database connection using the Open method of the connection object.
√ Begin a transaction using the Begin Transaction method of the connection object. This method provides us with a transaction object that we will use later to commit or rollback the transaction. Note that changes caused by any queries executed before calling the Begin Transaction method will be committed to the database immediately after they execute.Set the Transaction property of the command object to the above mentioned transaction object.
√ Execute the SQL commands using the command object. We may use one or more command objects for this purpose, as long as the Transaction property of all the objects is set to a valid transaction object.
√ Commit or roll back the transaction using the Commit or Rollback method of the transaction object.
√ Close the database connection.

(I)What’s difference between Dataset.clone and Dataset. copy ?
Clone: - It only copies structure, does not copy data.
Copy: - Copies both structure and data.

(A)Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?
There two main basic differences between recordset and dataset :-
√ With dataset you an retrieve data from two databases like oracle and sql server and merge them in one dataset , with recordset this is not possible
√ All representation of Dataset is using XML while recordset uses COM.
√ Recordset can not be transmitted on HTTP while Dataset can be.