应用过滤器时ef核心的怪异问题

Question

I have a very weird problem. I have noticed that this problem is caused only when a filter is applied. (check comments in the code for more info)

Stack trace: Code:

if (!string.IsNullOrEmpty(searchTerm)) // If that pass only then i got exception!
{
    query = query.Where(FilterBySearchTerm2(searchTerm));
}

var count = await query.CountAsync(); // here is the exception
var totalPages = (int)Math.Ceiling(count / (double)Pagination.DefaultPageSize);

-- Filter method

private Expression<Func<User, bool>> FilterBySearchTerm(string searchTerm)
{
    return u => u.FirstName.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.MiddleName.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.LastName.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.FullName.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase) // FullName is NotMapped property in the User class!
        || u.Company.Name.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.Email.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.Address.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.IncorporationNumber.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.DirectorFullName.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.DirectorEmail.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.DirectorPhone.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Phone.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Email.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)
        || u.Company.CompanyPrograms.Any(cp => cp.Program.Name.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase));
        }

-- FullName property in User class

 [NotMapped]
 public string FullName => string.IsNullOrEmpty(this.MiddleName) ?
      $"{this.LastName} {this.FirstName}" :
      $"{this.LastName} {this.FirstName} {this.MiddleName}";

That seems to be very deep in entity framework core, but I don't know if that's a bug or its expected to work like that.

UPDATE I have tested with simpler expression and I found the following:

Don't work:

 return u => u.FirstName.Contains(searchTerm, StringComparison.InvariantCultureIgnoreCase)

Work:

 return u => u.FirstName.Contains(searchTerm)

Work:

 return u => u.FullName.Contains(searchTerm)

Don't work:

return u => u.FirstName.Contains(searchTerm) 
     || u => u.MiddleName.Contains(searchTerm)
     || u => u.LastName.Contains(searchTerm) 
     || u => u.FullName.Contains(searchTerm) 

Answer 1

I am going to try to explain it as simple as i can..

First, please make sure that the values you are applying the filter to are not null .

Because if you try to call a function over a null value such an exception would be thrown.

Eg:

var keyword = "some key word";
string firstName = "John";
string lastName = null;

if(firstName.contains(keyword, StringComparison.InvariantCultureIgnoreCase)){
     //No exception would be thrown,
     //because it is like "john".contains("some key word", StringComparison.InvariantCultureIgnoreCase)
}


if(lastName.contains(keyword, StringComparison.InvariantCultureIgnoreCase)){
     //An exception would be thrown,
     //because it is like null.contains("some key word", StringComparison.InvariantCultureIgnoreCase)
}

The reason why FullName works is that because it is a combination of (FirstName, MiddleName, and LastName) and i am sure it is space-separated so the FullName would never be null , if all the combined propitiates are null it would be like .

string firstName = null;
string lastName = null;
var fullName = $"{firstName} {lastName}"; //or fullName = firstName + " " + lastName;

if(fullName.contains(keyword, StringComparison.InvariantCultureIgnoreCase)){
     //No exception would be thrown,
     //because it is like "  ".contains("some key word", StringComparison.InvariantCultureIgnoreCase)
}

---

Update: IMO you do not need to apply the filter to (FirstName, MiddleName, and LastName) because their values are within the FullName so you can remove the check condition for those and keep FullName with the rest of the filter.