Entity Framework with LINQ query

Question

What is difference between change / change2?

using (var context = new NORTHWNDEntities())
{
    var change = context.Regions.Where(r => r.RegionDescription == "East").ToList();

    var change2 = (from r in context.Regions where r.RegionDescription == "East" select new {r.RegionID, r.RegionDescription }).ToList();

    foreach (var p in change2)
    {
        p.RegionDescription = "West";
    }
    context.SaveChanges();
}

When I trying to make update on change2 in foreach loop i got error:

Property or indexer '......' cannot be assigned to -- it is read only

It works on previous version with lambda. How Can i change it to work?

Sounds like RegionDescription is a read only property... What about the error is confusing you? It does not work in the lambda either since the lamda is checking equality (==), not performing assignment (=) — maccettura
– maccettura, Commented Jun 21, 2018 at 19:25
You also returned an anonymous type in the 2nd version. You need to return an actual object if you want to change the values. — TyCobb
– TyCobb, Commented Jun 21, 2018 at 19:26

TyCobb · Accepted Answer · 2018-06-21 19:31:19Z

2

 var change2 = (from r in context.Regions 
                where r.RegionDescription == "East" 
                select new {r.RegionID, r.RegionDescription }).ToList();

You are returning an anonymous type. Anonymous type properties are read-only. If you want to change the value, you need to return an actual type that you have defined.

You can either new something else like new Region or just return r

var change2 = (from r in context.Regions 
                where r.RegionDescription == "East" 
                select r).ToList(); 


 var change2 = (from r in context.Regions 
                where r.RegionDescription == "East" 
                select new Region {.RegionID = r.RegionID, 
                                   .RegionDescription = r.RegionDescription }).ToList();

answered Jun 21, 2018 at 19:31

TyCobb

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2 Comments

Danki Over a year ago

Thank you for answer and explanation, it works perfect! :)

TyCobb Over a year ago

@Danki Glad it worked out. Please mark Answered on one of the submissions.

Johnathan Barclay · Accepted Answer · 2018-06-21 19:31:55Z

1

change2 returns an anonymous type which is immutable. To amend the value, you need to write:

var change2 = (from r in context.Regions where r.RegionDescription == "East" select r).ToList();

Which is equivalent to change1.

answered Jun 21, 2018 at 19:31

Johnathan Barclay

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