Generating Sequence Numbers In LINQ Query
Table of Contents
- Generating sequence numbers in SQL
- Generating sequence numbers in C# LINQ
- Why didn’t we do it on the first LINQ query?
In general, we can write a stored procedure something like this in
SQL and then map this to a DTO or a ViewModel in C# so that we can get the sequence numbers along with the data.
But, this isn’t any good if we are using
Entity Framework. Let’s see what we can do to generate the sequence numbers in C#.
First, we’ll write our query with DB context to fetch the data we want.
var data = DbContext.TestTable
The above LINQ query just pulls Datacolumn1, Datacolumn2 from TestTable if executed. Now, to get another column with sequence number, we’ll just enumerate the results of the above LINQ query so that we’ll get the columns we want.
IEnumerable interface provides an overload of
SELECT which can do this.
Here is the
SELECT overload definition.
public static IEnumerable<TResult> Select<TSource, TResult>(
So, we’ll see how it’s done.
var withSequence = data.AsEnumerable()
As you can see in Line 01, we’ve enumerated the results from the LINQ to Entities and then we performed a
.Select() on the enumerated set.
The index will have a starting value of zero so we’ll increment it to make the indexing start from 1. It’s up to you.
Here is the result.
The first LINQ query is
IQueryable and it doesn’t have the overload of
.Select() that has an index. So, we have to enumerate the results and then add sequence. So, in order to do it, we’ve to first make the
IQueryable result to and
IEnumerable result (as we did this in our second query using
Thanks for reading.