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c#linq
Muhammad Nasir
Muhammad Nasir

Reputation: 2204

How does skip and take works in linq

i have following Linq query . its works well but the thing that seems confusing is how does skip() and take() function working in linq. here is my query 

(from GRD in _tblAcademicYears.GetQueryable()
             where GRD.SchoolID == intSchoolID                 
             select new AcademicYearsModel
             {
                 AcademicYearID = GRD.AcademicYearID,
                 SchoolID = GRD.SchoolID,
                 AcademicYearName = GRD.AcademicYearName,
                 AcademicYearStart = GRD.AcademicYearStart,
                 AcademicYearEnd = GRD.AcademicYearEnd,
                 AcademicYearRemarks = GRD.AcademicYearRemarks,
                 IsActive = GRD.IsActive,
                 CreatedOn = GRD.CreatedOn,
                 CreatedBy = GRD.CreatedBy,
                 ModifiedOn = GRD.ModifiedOn,
                 ModifiedBy = GRD.ModifiedBy
             }
    ).Where(z => z.AcademicYearName.Contains(param.sSearch) || z.AcademicYearStart.ToString().Contains(param.sSearch)
    || z.AcademicYearEnd.ToString().Contains(param.sSearch) || z.AcademicYearRemarks.Contains(param.sSearch))
  .Skip(param.iDisplayStart).Take(param.iDisplayLength).ToList();

How this query will get record from data base . will it get all record from database and then will apply skip() and take(). or it will just get record that are with in limits of skip() and take()

Upvotes: 0

Views: 2732

Answers (3)

Harald Coppoolse
Harald Coppoolse

Reputation: 30464

The source code of all Linq IEnumerable extensions can be found here: System.Linq.Enumerable

Here you can see how skip and take work

Upvotes: 1

Backs
Backs

Reputation: 24903

If you asking about LINQ to SQL, you can run a sql-profiler to get query, generated by linq provider. But I can tell you, LINQ will get only records in limits skip and take, using row_number operator in SQL:

The query will be like this (skip 3 and take 3):

SELECT TOP (3) 
[Extent1].[ID] AS [ID], 
[Extent1].[Name] AS [Name], 
FROM ( 
    SELECT 
    [Extent1].[ID] AS [ID], 
    [Extent1].[Name] AS [Name], 
    row_number() OVER (ORDER BY [Extent1].[Name] ASC) AS [row_number]
    FROM [dbo].[tec_Stores] AS [Extent1]
)  AS [Extent1]
WHERE [Extent1].[row_number] > 3
ORDER BY [Extent1].[Name] ASC

In LINQ to Entities it works different, depending on collection you use.

Upvotes: 2

sowen
sowen

Reputation: 1088

When you call .Take only, it will just translate to SQL: TOP N syntax

When you call .Skip and .Take together, it will generate at least 2 queries, by using ROWNUMBER to filter out.

So the short answer for your question is: No, it will not get all records from database. it will run a SQL to filter and select.

If you are curious, you can always use SQL profiler or just check the generated SQL in the debug mode.

Here is a simple MSDN article explains it https://msdn.microsoft.com/library/bb386988(v=vs.100).aspx

Upvotes: 6

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