.NET Core 表达式 DbFunctions DiffDays

Question

我有一个我为日期过滤器编写的扩展，它使用 .NET 的 DiffDays 方法。 在 .NET Core 中，EF.Functions 被 DbFunctions 取代，所以无法执行。

我的 .NET 代码

 private static (ParameterExpression param, MemberExpression prop) QueryExpressions<Entity>(IQueryable<Entity> query, string property)
        {
            var param = Expression.Parameter(query.ElementType, "x");
            MemberExpression prop;

            if (property.Contains('.'))
            {
                string[] childProperties = property.Split('.');

                prop = Expression.Property(param, childProperties[0]);

                for (int i = 1; i < childProperties.Length; i++)
                    prop = Expression.Property(prop, childProperties[i]);
            }
            else
                prop = Expression.Property(param, property);

            return (param, prop);
        }

 public static IQueryable<Entity> DiffDaysLessThan<Entity>(this IQueryable<Entity> query, string property, object value)
        {
            var methodInfo = typeof(DbFunctions).GetMethod("DiffDays", new Type[] { typeof(DateTime?), typeof(DateTime?) });

            (ParameterExpression param, MemberExpression prop) = QueryExpressions(query, property);

            var left = Expression.Call(
                methodInfo,
                Expression.Convert(Expression.Constant(value), typeof(DateTime?)), Expression.Convert(prop, typeof(DateTime?)));
            var right = Expression.Convert(Expression.Constant(0), typeof(int?));

            var body = Expression.LessThanOrEqual(left, right);

            return query.Where(Expression.Lambda<Func<Entity, bool>>(body, param));
        }

.NET 核心

   public static IQueryable<Entity> DiffDaysLessThan<Entity>(this IQueryable<Entity> query, string property, object value)
        {

            var methodInfo = typeof(SqlServerDbFunctionsExtensions).GetMethod("DateDiffSecond", new Type[] { typeof(DbFunctions), typeof(DateTime?), typeof(DateTime?) });

            (ParameterExpression param, MemberExpression prop) = QueryExpressions(query, property);

            var left = Expression.Call(
                methodInfo,
                Expression.Convert(Expression.Constant(value), typeof(DateTime?)), Expression.Convert(prop, typeof(DateTime?)));
            var right = Expression.Convert(Expression.Constant(0), typeof(int?));

            var body = Expression.LessThanOrEqual(left, right);

            return query.Where(Expression.Lambda<Func<Entity, bool>>(body, param));
        }

在调用方法时，我不能等于 Expression.Call 端的 typeof (DbFunctions) 参数。

错误

System.ArgumentException：为调用方法“System.Nullable1[System.Int32] DateDiffSecond(Microsoft.EntityFrameworkCore.DbFunctions, System.Nullable1[System.DateTime], System.Nullable`1[System.DateTime])”（参数“方法”）提供的参数数量不正确

Answer 1

EF Core 函数是由EF.Functions 属性返回的DbFunctions 类的扩展 方法。因此，尽管未使用，但您必须在调用它们时传递DbFunctions 类型的第一个参数，例如

var left = Expression.Call(
    methodInfo,
    Expression.Constant(EF.Functions, typeof(DbFunctions)), // <--
    Expression.Convert(Expression.Constant(value), typeof(DateTime?)),
    Expression.Convert(prop, typeof(DateTime?)));