类型'System.Int32'的表达式不能用于方法'Boolean Equals(System.Object)'的'System.Object'类型的参数

Question

我有一个共同的网格视图柱过滤方法与的ColumnName和SEARCHTEXT明智滤波器网格视图记录.在这里,当我在可空INT DataColumn的操作也有像这个方法抛出错误:

类型'System.Int32'的表达式不能用于方法'Boolean Equals(System.Object)'的'System.Object'类型的参数

我的方法代码是:

 public static IQueryable<T> FilterForColumn<T>(this IQueryable<T> queryable, string colName, string searchText)
{
    if (colName != null && searchText != null)
    {
        var parameter = Expression.Parameter(typeof(T), "m");
        var propertyExpression = Expression.Property(parameter, colName);
        System.Linq.Expressions.ConstantExpression searchExpression = null;
        System.Reflection.MethodInfo containsMethod = null;
        // this must be of type Expression to accept different type of expressions
        // i.e. BinaryExpression, MethodCallExpression, ...
        System.Linq.Expressions.Expression body = null;
        Expression ex1 = null;
        Expression ex2 = null;
        switch (colName)
        {
            case "JobID":
            case "status_id":
                Int32 _int = Convert.ToInt32(searchText);
                searchExpression = Expression.Constant(_int);
                containsMethod = typeof(Int32).GetMethod("Equals", new[] { typeof(Int32) });
                body = Expression.Call(propertyExpression, containsMethod, searchExpression);
                break;
            case "group_id":
                Int32? _int1 = Convert.ToInt32(searchText);
                searchExpression = Expression.Constant(_int1);
                containsMethod = typeof(Int32?).GetMethod("Equals", new[] { typeof(Int32?) });                     
                //Error throws from this line
                body = Expression.Call(propertyExpression, containsMethod, searchExpression);


                break;
            case "FileSize":
            case "TotalFileSize":
                Int64? _int2 = Convert.ToInt64(searchText);
                searchExpression = Expression.Constant(_int2);
                containsMethod = typeof(Int64?).GetMethod("Equals", new[] { typeof(Int64?) });
                body = Expression.Call(propertyExpression, containsMethod, searchExpression);
                break;
            // section for DateTime? properties
            case "PublishDate":
            case "Birth_date":
            case "Anniversary_date":
            case "Profile_Updated_datetime":
            case "CompletedOn":
                DateTime currentDate = DateTime.ParseExact(searchText, "dd/MM/yyyy", null);
                DateTime nextDate = currentDate.AddDays(1);
                ex1 = Expression.GreaterThanOrEqual(propertyExpression, Expression.Constant(currentDate, typeof(DateTime?)));
                ex2 = Expression.LessThan(propertyExpression, Expression.Constant(nextDate, typeof(DateTime?)));
                body = Expression.AndAlso(ex1, ex2);
                break;
            // section for DateTime properties
            case "Created_datetime":
            case "Reminder_Date":
            case "News_date":
            case "thought_date":
            case "SubscriptionDateTime":
            case "Register_datetime":
            case "CreatedOn":
                DateTime currentDate1 = DateTime.ParseExact(searchText, "dd/MM/yyyy", null);
                DateTime nextDate1 = currentDate1.AddDays(1);
                ex1 = Expression.GreaterThanOrEqual(propertyExpression, Expression.Constant(currentDate1));
                ex2 = Expression.LessThan(propertyExpression, Expression.Constant(nextDate1));
                body = Expression.AndAlso(ex1, ex2);
                break;
            default:
                searchExpression = Expression.Constant(searchText);
                containsMethod = typeof(string).GetMethod("Contains", new[] { typeof(string) });
                body = Expression.Call(propertyExpression, containsMethod, searchExpression);
                break;
        }
        var predicate = Expression.Lambda<Func<T, bool>>(body, new[] { parameter });
        return queryable.Where(predicate);
    }
    else
    {
        return queryable;
    }
}

这是我解雇的问题:

var query = Helper.GetUsers().Where(u => u.Id != user_id).OrderByDescending(u => u.Register_datetime).Select(u => new
                  {
                      Id = u.Id,
                      Name = u.First_name + " " + u.Last_name,
                      IsActive = u.IsActive,
                      IsVerified = u.IsVerified,
                      Username = u.Username,
                      password = u.password,
                      Birth_date = u.Birth_date,
                      Anniversary_date = u.Anniversary_date,
                      status_id = u.status_id,
                      group_id = u.group_id,
                      Profile_Updated_datetime = u.Profile_Updated_datetime,
                      Register_datetime = u.Register_datetime
                  }).FilterForColumn(ColumnName, SearchText).ToList();

在这里,我有我的query.GetType().toString()方法得到更好地理解类型,我就可以运行列.

System.Collections.Generic.List`1[<>f__AnonymousType0`12[System.Int32,System.String,System.Boolean,System.Boolean,System.String,System.String,System.Nullable`1[System.DateTime],System.Nullable`1[System.DateTime],System.Int32,System.Nullable`1[System.Int32],System.Nullable`1[System.DateTime],System.DateTime]]

Answer 1

编辑

在这个问题中找到了解决方案.您需要Object在调用Equals(object)方法之前将表达式转换为:

var converted = Expression.Convert(searchExpression, typeof(object));
body = Expression.Call(propertyExpression, containsMethod, converted);

Nicodemus13建议首先明确设置searchExpression类型也Object应该有效.

原版的

我还没有找到问题,但我使用Linqpad在SSCCE中重现了这个问题:

void Main()
{
    var myInstance = new myClass();
    var equalsMethod = typeof(Int32?).GetMethod("Equals", new[] { typeof(Int32?) });
    int? nullableInt = 1;
    var nullableIntExpr = System.Linq.Expressions.Expression.Constant(nullableInt);
    var myInstanceExpr = System.Linq.Expressions.Expression.Constant(myInstance);
    var propertyExpr = System.Linq.Expressions.Expression.Property(myInstanceExpr, "MyProperty");
    var result = Expression.Call(propertyExpr,equalsMethod,nullableIntExpr); // This line throws the exception.
    Console.WriteLine(result);
}

class myClass{public int? MyProperty{get;set;}}

这一行:

containsMethod = typeof(Int32?).GetMethod("Equals", new[] { typeof(Int32?) });

返回MethodInfo方法的a Int32?.Equals (Object other).请注意,参数类型object不是Int32(或Int32?)正如您所料.

原因是typeof(Int32?)IS System.Nullable<Int32>,其中只有所述Equals(object)方法.