Basic ADO.NET Interview Questions

servletsinterviewquestions (1)ADO.NET is Microsoft’s latest technology for manipulating and access data objects either in the form of a databases such SQL Server, Oracle or Access, or general data sources such as text files, XML files and other file streams. Anyone looking to pursue a career in Microsoft’s application development technologies, mainly .NET, must have some experience and knowledge in ADO.NET. This article contains some of the most fundamental and frequently asked questions in any .NET-related job.

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Q1: What is ADO.NET?

Answer: ADO.NET stands for ActiveX Data Objects and is used to access and manipulate data services in Microsoft applications. ADO.NET interacts with data using a disconnected data set model and is mostly used for accessing relational databases.

Q2: What are some of the namespaces in ADO.NET that provide access to data?

Answer: There are three major namespaces used for interacting with data in ADO.NET

  • System.Data
  • System.Data.SQLClient
  • System.Data.OleDb

Q3: What is DataSet Object in ADO.NET?

Answer: The DataSet object is an in-memory representation of a data sources such as table records from a database. The DataSet object stores data in the form of rows and columns where each row represents a record and each column represent a particular value or property from that record.

Q4: What is an ADO.NET DataReader?

Answer: The DataReader object in ADO.NET is used to sequentially read data from an underlying data source. The DataReader object provides read-only access to data and cannot be used for DDL and DML operations.

Q5: What is LINQ?

Answer: LINQ stands for (Language Integrated Query) used for querying collections of data. LINQ queries can be executed on local collections such as types from System.Collections namespace and System.Collections.Generic namespace. LINQ queries can also be executed over LINQ to SQL and Entity framework classes that are used to interact with databases and other data sources that do not exist within the application domain, such as XML.

Q6: What is Object Pooling in ADO.NET?

Answer: In .NET, whenever functionality has to be performed, the Class that contains that functionality is instantiated. The object of the class is created, desired functionality is performed and then that object is destroyed. This process of creating and destroying objects is expensive. In ADO.NET objects are consistently created and destroyed as the application is connected to database, fetches records from database and disconnects from database. Therefore, the objects that are frequently used are placed in a pool from where they can be accessed whenever a related functionality needs to be performed. This phenomenon is known as object pooling.

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Q7: What is ADO.NET DataAdapter?

Answer: To perform communication between ADO.NET data sources such as databases and XML files and a DataSet, the DataAdapter object is used. All CRUD (create, read, update and delete) queries are performed using this DataAdapter.

Q8: Briefly mention some of the benefits of ADO.NET data access technology.

Answer: The following are some of the important benefits of using ADO.NET for data access:

  • ADO.NET objects are highly programmable and are flexible enough to be tweaked and twisted to achieve the desired functionality.
  • Code written in ADO.NET is highly maintainable and new data access features can be added to existing application imperceptibly.
  • ADO.NET objects are simple .NET objects that translate into MSIL code. Therefore, ADO.NET code written in one language can be seamlessly used with other .NET languages as well.
  • ADO.NET supports data scalability and is independent of the amount of data stored in the underlying database. Therefore, if data source expands or shrinks, the impact on the ADO.NET classes is minimal.

Q9: Differentiate between Boxing and Unboxing

Answer: The process of storing a value type into a reference type variable or object is known as boxing. Unboxing is the opposite of boxing and is referred to as the process of storing a reference type into a value type variable. In .NET, boxing is done implicitly, while a casting mechanism is required to achieve unboxing.

Q10: Do ADO.NET supports stored procedures?

Answer: Yes, ADO.NET contains a complete framework for executing stored procedures on a data set. Stored procedures in ADO.NET are used mostly for common repetitive functions.

Q11: What are the basic layers of any ADO.NET based data-centric application?

Answer: Every data-centric application that uses ADO.NET should ideally be structured into three layers.

  • Presentation layer: Provides all the GUI and interaction services to end user.
  • Business Logic Layer: Used to implement all the business logic of an application.
  • Data Access Layer: Provides types that are used to interact with the underlying databases.

Q12: Elaborate on some of the advantages of using stored procedures in ADO.NET.

Answer: The following are some of the benefits of implementing ADO.NET stored procedures:

  • Stored procedures reside in databases in compiled form. This results in extremely fast performance.
  • Stored procedures require less network traffic and bandwidth to execute on remote databases since they do not contain any extra information but only compiled data.
  • Stored procedures are secure and invulnerable to any outside threat data might result in loss or leakage of data.

Q13: Can data be edited in a repeater control?

Answer: No, the repeater data control is used to show data. Data cannot be edited in a repeater control. The DataGridView controls can be used for editing purposes.

Q14:  Briefly explain some of the components of ADO.NET Data providers:

Answer: The following are some of the most important components of ADO.NET data providers:

  • Connection: This is the object responsible for establishing a connection to the database.
  • Command: The object responsible for executing commands and stored procedures.
  • ExecuteReader: Returns a complete set of results
  • ExecuteScaler: Returns only a single value
  • ExecuteNonQuery: Execute a command on a database but it doesn’t return any value from the database. Used mostly for insertion and update.
  • DataReader: Provides read-only and forward-only access to a database.

This article contains some of the most fundamental and basic ADO.NET questions that can be asked in any .NET job interview. To study how ADO.NET can be used to develop data-centric applications, see this course.