EF Core LINQ Where 扩展方法未转换为 SQL

Question

Given the following query:

context.ToolingOrders
.Include(r => r.ToolingOrderDetails)
.Include(r => r.PurchaseOrder)
.Where(r => r.VendorId.EqualsOrNull(filter.VendorId) && 
            r.PoNumber.ContainsOrEmpty(filter.PoNumber))

I use these extension methods to save some code:

 public static class FilterExtensions
 {
        public static bool ContainsOrEmpty(this string source, string toCheck)
        {
            return string.IsNullOrWhiteSpace(toCheck) || source?.IndexOf(toCheck, StringComparison.OrdinalIgnoreCase) >= 0;
        }

        public static bool EqualsOrNull(this int source, int? toCheck)
        {
            return !toCheck.HasValue || source == toCheck;
        }
 }

The problem is, due to these extension methods, the Where part is not translated into SQL.

I use .Net Core 2.2, wich has this client side evaluation feature , which totally hides this issue, but the SQL profiler shows it anyway.

Is there any way to make this work, or I have to write every piece of the where part explicitly?

Answer 1

You could extend the IQueryable for your specific object.
Take the following object for instance:

public class MyObject
{
    public string MyProperty;
}

You could write an extension like this:

public static class MyQueryExtension
{
    public static IQueryable<MyObject> WhereMyPropertyNull(this IQueryable<MyObject> queryable)
    {
        return queryable.Where(obj => obj.MyProperty == null);
    }
}

And use it like this:

var queryable = new List<MyObject>().AsQueryable();
var result = queryable.WhereMyPropertyNull().ToList();

EDIT

Based on some feedback i updated my answer to handle generics.

public static class Extensions
    {
        public static IQueryable<TEntity> EqualOrNull<TEntity, TProperty>(this IQueryable<TEntity> source, Func<TEntity, TProperty> selector, TProperty match)
        {
            return source.Where(entity => Match(selector.Invoke(entity), match));
        }

        private static bool Match<TEntity, TProperty>(TEntity entity, TProperty match)
        {
            if (entity == null) {
                return true;
            } else {
                return entity.Equals(match);
            }
        }
    }

It can be used to pass the value of a property to the where statement:

            var list = new List<MyObject>();
            list.Add(new MyObject {MyProperty = "Test"});
            list.Add(new MyObject {MyProperty = "NoMatch"});
            list.Add(new MyObject {MyProperty = null});

            var result = list.AsQueryable()
                .EqualOrNull(o => o.MyProperty, "Test")
                .ToList();