LINQ Query if condition external parameter

Question

I'm trying to use LINQ to get a list of values.

I have code like this:

var _context = _scope.ServiceProvider.GetRequiredService<VMContext>();

if (boolparameter)
{
    var listCE = _context.Ce
                         .Where(x => x.VuId == element.VuId)
                         .Where(x => x.Score == 8)
                         .AsNoTracking()
                         .ToList();
}
else
{
    var listCE = _context.Ce
                         .Where(x => x.VuId == element.VuId)
                         .AsNoTracking()
                         .ToList();
}

Depends on boolparameter, I do a query or another one. Is there a way to use a single query with a conditions inside? Something like:

var listCE = _context.Ce
                     .Where(x => x.VuId == element.VuId)
                     .Where(x => boolparameter ? x.Score == 8 : true)
                     .AsNoTracking()
                     .ToList();

C# Asp.NetCore SqlServer 2019 Thanks a lot!

Other answers are good but maybe a bit hard to catch. I found this easier to understand. (boolparameter && x.Score==8) || !boolparameter. of course if you simplify this it will become like the answers given. — M.kazem Akhgary
– M.kazem Akhgary, Commented Jan 21, 2020 at 11:30

Nguyễn Văn Phong · Accepted Answer · 2020-01-22 01:22:27Z

6

You could try the following code if it works:

var listCE = _context.Ce
  .Where(x => x.VuId == element.VuId)
  .Where(x => !boolparameter || x.Score == 8)
  .AsNoTracking()
  .ToList();

Which means if boolparameter is false, x.Score doesn't matter, since !false would equal to true and it satisfies OR condition. Likewise if boolparameter is true, then x.score will also be checked if it is equal to 8.

Or maybe with one Where condition:

var listCE = _context.Ce
  .Where(x => x.VuId == element.VuId && (!boolparameter || x.Score == 8))
  .AsNoTracking()
  .ToList();

edited Jan 22, 2020 at 1:22

Nguyễn Văn Phong

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answered Jan 21, 2020 at 11:22

Jure

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Comments

Johnathan Barclay · Accepted Answer · 2020-01-21 11:23:40Z

1

var listCE = _context.Ce
    .Where(x =>
        x.VuId == element.VuId
        && (!boolparameter || x.Score == 8))
    .AsNoTracking()
    .ToList();

This checks whether boolparameter is true before checking x.Score.

answered Jan 21, 2020 at 11:23

Johnathan Barclay

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Comments

Nguyễn Văn Phong · Accepted Answer · 2020-01-22 01:23:39Z

1

Can you check that below?

var listCE = _context.Ce
        .Where(x => boolparameter == false ? x.VuId == element.VuId : 
        (x.VuId == element.VuId && 
        x.Score == 8)) 
        .AsNoTracking()
        .ToList();

edited Jan 22, 2020 at 1:23

Nguyễn Văn Phong

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answered Jan 21, 2020 at 11:23

umut

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Comments

Nguyễn Văn Phong · Accepted Answer · 2020-01-22 01:41:53Z

0

This way is more verbose, but if you have more (or complicated) conditions it can be easier to read and quickly understand what affects the query. LINQ doesn't execute the query until you reach .ToList() or otherwise try to access the result from the query.

This means you don't need to have the full query duplicated in both the if and else part:

var _context = _scope.ServiceProvider.GetRequiredService<VMContext>();

var listCEQuery = _context.Ce.Where(x => x.VuId == element.VuId)

// LINQ will append this to the initial where clause   
if (boolparameter == true)
    listCEQuery = listCEQuery.Where(x => x.Score == 8)

var listCE = listCEQuery.AsNoTracking().ToList();

edited Jan 22, 2020 at 1:41

Nguyễn Văn Phong

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answered Jan 21, 2020 at 11:29

lmms90

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