Call c# method in linq query(entity framework)

Question

Is there any chance to run c# method in linq query? I need to do something like that:

//...
class Match {
  public double PrecentageMatching(string s1, string s2) {
    //...
    return result; // value from 0.0 to 1.0
  }
}
//...

string pattern = "nameOfRecord";
var similarRecords = db.Table.Select( 
   r => Match.PrecentageMatching(r.name, pattern) > 0.5 
);

I know that there linq wont know a method PrecentageMatching. But I'm wonder if there is any way to do it?

I'm using Entity framework. I need to do it without stored procedures and assembly on database side. I dont have access to database.

Daniel Hilgarth · Accepted Answer · 2011-09-21 07:24:57Z

6

You first need to fetch the data from the database and only then perform the transformation:

string pattern = "nameOfRecord";
var similarRecords = db.Table
                       .Select(r => r.name)
                       .ToList() // This call fetches the data from the DB
                       .Select(x => Match.PrecentageMatching(x, pattern) > 0.5);

That's not a problem at all, because you are only transforming the returned data with your method. If you want to use your method to filter the returned data using Where, you have a problem, because you would first need to return ALL data and filter the data on your client. This might be a problem if the table is big.

edited Sep 21, 2011 at 7:24

answered Sep 21, 2011 at 7:15

Daniel Hilgarth

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2 Comments

nosbor Over a year ago

Its. Working. Thanks. And one another thing... is there any option to change this query that I can receive all fields? Because in your query i received only name field.

Daniel Hilgarth Over a year ago

Sure. Just remove the .Select(r => r.name) line and change the last line to .Select(x => Match.PrecentageMatching(x.name, pattern) > 0.5);.

Daryl Teo · Accepted Answer · 2011-09-21 07:30:24Z

2

Change your PrecentageMatching method to a static method. It will then be able to find Match.PrecentageMatching method.

Also, what you're doing there will return a IEnumerable of boolean values. If you want to return records from the Table, you want "Where" instead of "Select".

Edit: as per comments, you need to call ToList() method.

edited Sep 21, 2011 at 7:30

answered Sep 21, 2011 at 7:13

Daryl Teo

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4 Comments

Daniel Hilgarth Over a year ago

Good catch with the missing static, but that is not the problem here. The problem is that the EF data provider doesn't know how to translate Match.PercentageMatching into SQL code and will throw a runtime exception.

Daryl Teo Over a year ago

@DanielHilgarth didn't know that. sheepish I just use the basic stuff. Voted your answer.

nosbor Over a year ago

Yes. Daniel is right. This will compile but will not work. You will get an exception: "LINQ to Entities does not recognize the method 'Int32 LevensteinDistance(System.String, System.String)' method, and this method cannot be translated into a store expression."

Daniel Hilgarth Over a year ago

@Daryl: That's what we are here for :-)

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