EF Like 操作符用法

Question

I tried to use DbFunctions.Like with EF 6.2 and got run-time error:

LINQ to Entities does not recognize the method 'Boolean Like(System.String, System.String)' method, and this method cannot be translated into a store expression.

Code:

list=list.Where(p=> DbFunctions.Like(p.Master_Bill,"somestring%")); where list is IQueryable<SomeView>

It compiles OK. I thought it can be used with EF 6.2. I know there is also EF Core, did not look at it

Any ideas? thanks

Answer 1

What about

list = list.Where( p => p.Master_Bill.StartsWith(someString));

?

If the user can enter a wildcard(s) in their search string you can evaluate the string for legal combinations Ie "?somestring", "somestring?" or "?somestring?" then choose the appropriate where condition.

wildcardResult = evaluateWildcard(someString);
switch(wildcardResult.Result)
{
    case WildcardResult.NoWildcard:
        list = list.Where( p => p.Master_Bill == wildcardResult.SearchString);
        break;
    case WildcardResult.StartsWith:
        list = list.Where( p => p.Master_Bill.StartsWith(wildcardResult.SearchString));
        break;
    case WildcardResult.EndsWith:
        list = list.Where( p => p.Master_Bill.EndsWith(wildcardResult.SearchString));
        break;
    case WildcardResult.Contains:
        list = list.Where( p => p.Master_Bill.Contains(wildcardResult.SearchString));
        break;
}

Where the result class contains an enum for the detected search expression pattern, and the search expression with the wildcard characters stripped to use as the SearchString.

It would also be advisable to evaluate the length of the search string for a minimum viable length when using wildcards. Users could trigger rather expensive queries by using expressions like "?" or "?e?".

Edit: DbFunctions.Like does work as well with SQL Server. Any error you are getting is likely due to an assumption about the IQueryable you are running or the field you are comparing. (Ie not a mapped column, or a particular data type?)

For instance: Something like this works just fine..

var data = _context.People.Where(p => DbFunctions.Like(p.Name, "s%")).ToList();

Which would return all People with a Name starting with "S". (case insensitive)

I'd look at what your entire IQueryable looks like, as well as that Master_Bill is both a mapped column and a regular NVARCHAR/VARCHAR column.