LINQ syntax where string value is not null or empty

Question

I m trying to do a query like so     query Where x   gt   string IsNullOrEmpty x PropertyName      but it fails     so for now I have implemented the following  which works     query Where x   gt   x PropertyName    string Empty     string Empty     is there a better  more native   way that LINQ handles this   EDIT  apologize  didn t include the provider    This is using LINQ to SQL

User · Accepted Answer

http   connect microsoft com VisualStudio feedback ViewFeedback aspx FeedbackID 367077  Problem Statement It s possible to write LINQ to SQL that gets all rows that have either null or an empty string in a given field  but it s not possible to use string IsNullOrEmpty to do it  even though many other string methods map to LINQ to SQL  Proposed Solution Allow string IsNullOrEmpty in a LINQ to SQL where clause so that these two queries have the same result   var fieldNullOrEmpty   from item in db SomeTable where item SomeField    null    item SomeField Equals string Empty  select item   var fieldNullOrEmpty2   from item in db SomeTable where string IsNullOrEmpty item SomeField  select item    Other Reading  1  DevArt 2  Dervalp com 3  StackOverflow Post

User · Answer

This won t fail on Linq2Objects  but it will fail for Linq2SQL  so I am assuming that you are talking about the SQL provider or something similar   The reason has to do with the way that the SQL provider handles your lambda expression   It doesn t take it as a function Func lt P T gt   but an expression Expression lt Func lt P T gt  gt    It takes that expression tree and translates it so an actual SQL statement  which it sends off to the server   The translator knows how to handle basic operators  but it doesn t know how to handle methods on objects   It doesn t know that IsNullOrEmpty x  translates to return x    null    x    string empty   That has to be done explicitly for the translation to SQL to take place

User · Answer

This will work fine with Linq to Objects   However  some LINQ providers have difficulty running CLR methods as part of the query   This is expecially true of some database providers   The problem is that the DB providers try to move and compile the LINQ query as a database query  to prevent pulling all of the objects across the wire   This is a good thing  but does occasionally restrict the flexibility in your predicates   Unfortunately  without checking the provider documentation  it s difficult to always know exactly what will or will not be supported directly in the provider   It looks like your provider allows comparisons  but not the string check   I d guess that  in your case  this is probably about as good of an approach as you can get    It s really not that different from the IsNullOrEmpty check  other than creating the  string Empty  instance for comparison  but that s minor

[linq] LINQ syntax where string value is not null or empty

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