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What is disconnected data?
Answer: A data representation, such a DataSet, that doesn't require a continuous database connection. Working with disconnected data:
The data in DataSet is disconnected from database. Once you fetch the results of a query into a DataSet using a DataAdapter object, there is no longer a connection between DataSet and database. Changes you make to the contents of the DataSet will not affect the database. If other users modify data in database that corresponds to the data in DataSet, you will not see those changes in your DataSet.
Working with disconnected data structures definitely has its benefits. The first major benefit of working with disconnected data is that it does not require a live connection to your database. Once you've fetched the results of your query into a DataSet object, you can close the connection to your database and continue to work with the data in your DataSet.
Disconnected data structures such as DataSets are also helpful when you build multi-tiered applications. If your application uses business objects running on a middle-tier server to access database, business object needs to pass disconnected data structures to client application. The DataSet object is designed for use in such situations. You can pass the contents of a DataSet from one component to another. The component that receives the data can work with the information as a DataSet (if the component is built using the Microsoft .NET Framework) or as an XML document.
Explain the DataTable and Relationship between the DataTable, the DataRow, and the DataColumn.
Answer: A DataTable object represents a database table. A data table is a collection of columns and rows. The DataRow object represents a table row, and the DataColumn object represents a column of the table.
The Columns property of the DataTable object represents the DataColumnCollection, which is a collection of DataColumn objects in a DataTable. You use a DataRow object to add data to a data table. TheDataRowCollection object represents a collection of rows of a DataTable object, which can be accessed by its Rows property.
Explain about Data Access Object or DAO?
Answer: Data Access Object (DAO) enabled programmers to access local databases in the Microsoft Jet Database Engine format, which were primarily Indexed Sequential Access Method (ISAM) files. After DAO came RDO and then ActiveX Data Objects (ADO). These data access technologies were designed for a client / server paradigm. However the tendency of distributed computing forced the development of a new technology to solve the problems of data manipulation on a n-tier architecture. ADO.NET is the evolution of ADO and its components have been designed to function properly on a n-tier architecture.
What are the advantages of ADO.NET?
Answer: Advantages of ADO.NET:
ADO.NET offers several advantages over previous Microsoft data access technologies, including ADO. Few advantages are listed below:
Single Object-oriented API
ADO.NET provides a single object-oriented set of classes. There are different data providers to work with different data sources but the programming model for all these data providers work in the same way.
The ADO.NET classes are managed classes. CLR takes care of language independency and automatic resource management.
Microsoft uses MDAC (Microsoft Data Access Component), which is used as ActiveX component in .NET Framework (X is extensible component, when X is written after a term means extensible). .NET components takes care of deployment which was difficult than the previous technologies used in deployment.
ADO.NET data is cached and transferred in XML (EXtensible Markup Language) format. XML provide fast access of data for desktop and distributed applications.
Performance and scalability
Performance and scalability are two major factors while developing web-based application and services. Disconnected cached data in XML help in performance and scalability.
How can you access the data from DataReader?
Answer: DataReader is a class that holds data as rows and coloums to access data from the DataReader.
It provides the following methods:
1. GetName(int ColIndex)
The return type of this method is a string, it returns the name of the column for the given index position.
Moves the Record Pointer from the current location to the next row and returns a Boolean status that tells whether the row to which we have moved contains data in it or not, that will be true if present or false if not present.
3. GetValue(int Colindex)
Returns a column's value from the row to which the pointer was pointing by specifying the column index position.
4. NextResult ()
Moves the record pointer from the current table to the next table if a table exists and returns true else returns false.
Features of Data Reader
1. Provides faster access to data from a Data Source, since it is connection oriented.
2. It can hold multiple tables at a time. To load multiple tables into a DataReader pass multiple select statements as the argument to the command separated by a colon (;).
1. Command cmd=new Command(“Select * From Student ; Select * From Mark ”, Con);
2. Data Reader dr= cmd.ExecuteReader();
Question 50: What is BindingSource class in ADO.NET?
Answer: The BindingSource class is used to simplify data binding as well as various operations on records. It has different methods like AddNew( ), MoveFirst( ), MovePrevious( ), MoveNext( ), etc which provide easier way for adding new row, moving to first record, moving to previous record, moving to next record and many other operations without writing code for them.
Q #1) What is ADO.NET?
Answer: ADO.net Stands for Microsoft ActiveX Data Object. Ado.net is a database technology which we can think like a set of classes that can be used to interact with the data sources like databases and XML files.
Asp.net application, windows application, console application are the few types of .net applications that use ADO.NET to connect with the databases to execute commands and retrieve data.
Q #2) What are the key features of ADO.NET?
• Disconnected Data Architecture.
• Data cached in DataSet.
• Data transfer in XML Format.
• Strongly typed language.
Q #3) Why is it important to close an ADO.NET application?
Answer: Connections need to be closed properly because it affects the scalability and reliability of the applications.
For open connections it is always vulnerable to attack, so to be short, ‘Open connections as late as possible and close it as early as possible’. We can ‘Close’ the connections by ‘final’ block or ‘using’ the USING statement.
Q #4) What are the two uses of a ‘using’ statement in c#?
#1) To import a namespace.
For Example: using System;
#2) To Close a connection properly, refer the below figure. The connection is automatically closed at the end of ‘using’ block.
Q #5) Give an example of a .NET application which connects to Microsoft Access Database using Ado.net classes. Answer: Example given below describes only how to establish a connection to Microsoft Access Database, it won’t explain about the executing commands against the database.
For establishing a connection to the database and retrieve the values from a database we need to follow the below steps:
• Import reference library class. Example: using System.Data.OleDB.
• Create connection object.
• Specify the connection string, you may copy that from the Database Property.
• Use Connection object constructor and specify the ‘connection String ‘as Argument.
• Open an instance of Connection (It’s better to open it in a try-catch statement).
Q #6) What is Connection Pooling?
Answer: Data providers implement ‘Connection pooling’ services. ‘Connection pooling’ improves performance. Connection pooling creates a set of connections.
When you are establishing a connection with the database, you will be given a connection from a pool. When you disconnect from the database, the connection will return to the pool and that connection will be used by the next applicant who wants a connection.
With ‘Connection pooling’ the ‘opening’ and ‘closing’ of connections no longer become an expensive task.
Q #7) What is a Dataset?
Answer: Dataset is a disconnected copy of data that gets populated in the client PC. It contains Datatables and Datarelations. Generally, DataAdapter is required for populating a Dataset with the data.
Since it is disconnected, the user no longer need to be connected to the database every time and data manipulations are performed without interacting with the data source. It is very fast and reliable as it resides in the local system.
Two Objects in Dataset
Two Types of Dataset
• Typed Dataset
• Untyped Dataset
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