c# - Entity Framework core - Contains is case sensitive or case insensitive?

Question

"Contains" in Entity Framework core should equivalent to the SQL %like% operator. Therefore "Contains" should be case insensitive however it is case sensitive! (at least in postgres????)

The following only outputs a result when the correct casing for keyword is used.

context.Counties.Where(x => x.Name.Contains(keyword)).ToList();

What am I doing wrong?

Answer 1

It used to be the case for older versions of EF core. Now string.Contains is case sensitive, and for exemple for sqlite it maps to sqlite function `instr()' ( I don't know for postgresql).

If you want to compare strings in a case-insensitive way, you have DbFunctions to do the jobs.

context.Counties.Where(x => EF.Functions.Like(x.Name, $"%{keyword}%")).ToList();

UPDATE to @Gert:

A part of the assumption in the question is incorrect. string.Contains does NOT convert into a LIKE expression even though it USED to be the case in ef core versions <= 1.0 (I think).

• In SQLServer string.contains converts into CHARINDEX(), in oracle and sqlite into instr() which are case sensitive by default UNLESS db or column collation is defined otherwise ( Again, I don't know for postgresql ).
• In all cases EF.Functions.Like() converts into a SQL LIKE expression which is case-insensitive by default unless db or column collation is defined otherwise.

So yes it all goes down to collation but - correct me if I'm wrong - in a way the code can have an influence on the case-sensitive/insensitive search depending on which one of the above method you use.

Now, I might not be completely up to date but I don't think EF core migrations deal with DB collation naturally and unless you've already created the table manually you will end up with the default collation (case-sensitive for sqlite and I honestly don't know for the others).

Getting back to the original question you have at least 2 options to perform this case-insensitive search if not 3 in a future release :

1. Specify the column collation on creation using DbContext.OnModelCreating() using this trick
2. Replace your string.Contains by EF.Functions.Like()
3. Or wait for a promising feature still in discussion : EF.Functions.Collate() function