C# check string contain a word with underscores

Question

I want to get all items which contain " _AT_ " or " PV_ ", but d.Nom.Contains($"PV_") and d.Nom.Contains($"_AT_") gets also items containing only "AT" and "PV"

 IQueryable<DocumentMetadata> docPV = NHibernateSession.Current.Query<DocumentMetadata>()
           .Where(d => d.IdEntiteRattachement == missionId
                       && d.Nom.Contains($"PV_")
                       && d.Desactive == false)
           .OrderByDescending(d => d.DateDerniereModif);

        IList<DocumentMetadata> docAR = NHibernateSession.Current.Query<DocumentMetadata>()
           .Where(d => d.IdEntiteRattachement == missionId
                       && d.Nom.Contains($"_AT_")
                       && d.Desactive == false)
           .OrderByDescending(d => d.DateDerniereModif).ToList();

Answer 1

In SQL, underscore (and percent) are wild cards. NHibernate doesn't automatically escape them, because you can make use of them. Behind .Contains , there is SQL's LIKE .

Escaping wildcards depend on the underlying DBMS.

Try this:

d.Nom.Contains("\\_AT\\_")

(It may not work. See the docs of your database engine.)

Answer 2

Somehow none of the solutions given above would escape the underscore properly (I tried \\\\_ @\\_ [_] $_ ^_ ) so I ended up filtering again in pure LINQ:

var list = dc.Employees.Where(a => a.Name.Contains(partial)).ToList();
if (partial.Contains("_")) // underscore is an sql wildcard character and will match anything, so filter again in .NET linq
    list = list.Where(a => a.Name.Contains(partial)).ToList();

This is obviously not the best solution since it retrieves a bigger amount of rows from the DB than necessary and filters again in memory, but in my case the overhead is acceptable.