Background

I am a dot net developer. As a dot net developer, you will always use ADO.NET to handle your data. Isn’t it. So it is important that you must know some information. We will read those basic information here. I am sharing those in the form of articles, you can always read my other interview questions here in the below links.

So shall we now discuss about ADO.NET interview questions?

ADO.NET Interview Questions

What is ADO.NET?

ADO.NET is basically a set of components which can be used by a programmer to access and manipulate the data in a disconnected architecture. It gives the access to the data source such as SQL Server and XML. We use DataSet for the data operations in ADO.NET. It is a part of Microsoft .Net framework.

Difference between ExecuteReader, ExecuteScalar and ExecuteNonQuery ?

Source http://www.aspsnippets.com/Articles/Difference-between-ExecuteReader-ExecuteScalar-and-ExecuteNonQuery.aspx

ExecuteNonQuery

ExecuteNonQuery is basically used for operations where there is nothing returned from the SQL Query or Stored Procedure. Preferred use will be for INSERT, UPDATE and DELETE Operations.

[csharp]
using (SqlConnection con = new SqlConnection(constring))
{
using (SqlCommand cmd = new SqlCommand("DELETE FROM Persons WHERE Name = @Name", con))
{
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@Name", name);
con.Open();
int rowsAffected = cmd.ExecuteNonQuery();
con.Close();
}
}
[/csharp]

Execute Scalar

ExecuteScalar is a handy function when you want to just need one Cell value i.e. one column and one row.
For example in a case where I need to get the City of a person based on its Name.

[csharp]
using (SqlConnection con = new SqlConnection(constring))
{
using (SqlCommand cmd = new SqlCommand("SELECT City FROM Persons WHERE Name=@Name", con))
{
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@Name", name);
con.Open();
object o = cmd.ExecuteScalar();
if (o != null)
{
string city = o.ToString();
}
con.Close();
}
}
[/csharp]

Execute Reader

ExecuteReader is strictly used for fetching records from the SQL Query or Stored Procedure i.e. SELECT Operation.
Example would be fetching Name City for all records in the Person Table.

[csharp]
using (SqlConnection con = new SqlConnection(constring))
{
using (SqlCommand cmd = new SqlCommand("SELECT Name, City FROM Persons", con))
{
cmd.CommandType = CommandType.Text;
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
string name = dr["Name"].ToString();
string city = dr["City"].ToString();
Response.Write("Name: " + name);
Response.Write("City: " + city);
}
con.Close();
}
}
[/csharp]

What are Data Reader, Dataset & Data Adapter ? Explain the differences?

Data Reader

Data Reader is used to read the data from database and it is a read and forward only connection oriented architecture during fetch the data from database. Data Reader is used to iterate through result set that came from server and it will read one record at a time because of that memory consumption will be less and it will fetch the data very fast when compared with dataset. Generally we will use Execute Reader object to bind data to data reader.

[csharp]
using (SqlConnection con = new SqlConnection("Connectionstring"))
{
con.Open();
SqlCommand cmd = new SqlCommand("Select UserName,LastName,Location FROM UserInformation", con);
SqlDataReader dr = cmd.ExecuteReader();
}
[/csharp]

Dataset

Dataset is a disconnected orient architecture that means there is no need of active connections during work with datasets and it is a collection of Data Tables and relations between tables. It is used to hold multiple tables with data. You can select data form tables, create views based on table and ask child rows over relations. Also Dataset provides you with rich features like saving data as XML and loading XML data.

[csharp]
SqlCommand cmd = new SqlCommand("select UserName,LastName,Location from UserInformation", con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
[/csharp]

Data Adapter

DataAdapter will acts as a Bridge between DataSet and database. This dataadapter object is used to read the data from database and bind that data to dataset. Dataadapter is a disconnected oriented architecture.

[csharp]
SqlCommand cmd = new SqlCommand("select UserName,LastName,Location from UserInformation", con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
[/csharp]

ADO stands for?

ActiveX Data Object

What are the main objects used in ADO.NET?

Dataset

Dataset is a disconnected orient architecture that means there is no need of active connections during work with datasets and it is a collection of Data Tables and relations between tables. It is used to hold multiple tables with data. You can select data form tables, create views based on table and ask child rows over relations. Also Dataset provides you with rich features like saving data as XML and loading XML data.

DataReader

Data Reader is used to read the data from database and it is a read and forward only connection oriented architecture during fetch the data from database. Data Reader is used to iterate through result set that came from server and it will read one record at a time because of that memory consumption will be less and it will fetch the data very fast when compared with dataset. Generally we will use Execute Reader object to bind data to data reader.

That’s all. Have a great day.

Conclusion

Did I miss anything that you may think which is needed? Could you find this post as useful? I hope you liked this article. Please share me your valuable suggestions and feedback.

Your turn. What do you think?

A blog isn’t a blog without comments, but do try to stay on topic. If you have a question unrelated to this post, you’re better off posting it on C# Corner, Code Project, Stack Overflow, Asp.Net Forum instead of commenting here. Tweet or email me a link to your question there and I’ll definitely try to help if I can.

Kindest Regards
Sibeesh Venu

Introduction

Hi, I hope you are all fine. If you are a .Net professional and if you are looking for a change in job (especially in Infosys, IBM, DELL, Aversan) you may want to read: Interview Questions For 3 Year .NET Professionals.

I have described my interview experience there. Now I will share some other important series of questions that will definitely ask in any .Net interview. What employers currently look for in a candidate is logical understanding with basic knowledge. So understanding the basics is very important, even if you are an experienced candidate.

So let us start. I hope you will like this article. Please provide your valuable comments so that I can improve myself.

First of all you must be ready to introduce yourself. Please don’t use so many “mmmmm” and “And and and”. Be confident and don’t urge. Take your own time to describe yourself. Look straight. You can find more tips here: How to Prepare for a Job Interview.

Now we will concentrate on the technical questions.

Please note that these questions are asked in my interview experience, you may need to see more questions when you go for your interview.

1. What is the sequence of execution of the ASP.NET page life cycle?

The simple way is to remember SILVER.

S (It is not counted)
I (Init)
L (Load)
V (Validate)
E (Event)
R (Render)

Read more here.

2. What is the difference between a Hash Table and a Dictionary?

The main differences are listed below.

Dictionary:

Returns an error if the key does not exist
No boxing and unboxing
Faster than a Hash table

Hashtable:

Returns NULL even if the key does not exist
Requires boxing and unboxing
Slower than a Dictionary

3. How to use View state?

4. What are the state management techniques used in .NET?

Client-side:

• Hidden Field
• View State
• Cookies
• Control State
• Query Strings

Server-side:

Session

• In Proc mode
• State Server mode
• SQL Server mode
• Custom mode

Application.

Read here.

5. How can we create a new table in SQL with only the structure?

Here is the query to do that.

Points to be noted:

A is the source table.
B is the destination table.
The condition 1=2 is to prevent the data from being copyied.

6. How to add a button dynamically to a grid view?

7. How to find a control inside a GridView?

Here we are finding the control myButton from the 0th row first cell.

8. What are abstract and interface? Provide actual examples.

Please read here.

9. What is partial class?

There are the following situations of when splitting a class definition is desirable:
To work with large projects.
To split the class definitions as we needed with the keyword partial.

10. How to use a partial class?

11. How to remove a constraint from a table in SQL Server?

12. How to create Table Variables In T-SQL?

Normally the syntax to create a table variable is the same as to create a table statement.

13. How can you delete a duplicate record from a table in SQL?

There are so many ways to do this. Here I am sharing what I use when I get that kind of situation.

• I will create a temp table.
• Copy the distinct data from the existing table to the temp table.
• Empty the data in the existing table.
• Insert the data from the temp table to the source table.

Here is the query to do that:

14. When to use an override and new in C#?

We can use override when there is virtual/abstract/override type of method in base class. We can use New when there is no virtual/abstract/override type of method in base class.

Conclusion

Did I miss anything that you may think which is needed? Could you find this post as useful? I hope you liked this article. Please share me your valuable suggestions and feedback.

Your turn. What do you think?

A blog isn’t a blog without comments, but do try to stay on topic. If you have a question unrelated to this post, you’re better off posting it on C# Corner, Code Project, Stack Overflow, Asp.Net Forum instead of commenting here. Tweet or email me a link to your question there and I’ll definitely try to help if I can.

Kindest Regards
Sibeesh Venu