动态创建LINQ语句

Question

我正在使用带有大量可为空的布尔值的数据传输对象（名为SearchSpec）...

...
public bool? AL { get; set; }
public bool? TL { get; set; }
...

...使用LINQ从表中过滤数据...

var query = (from wv in Source select row); //Init query

if (SearchSpec.AL != null)
{
    query = (from wv in query
             where (wv.AL == SearchSpec.AL)
             select wv);
}

if (SearchSpec.TL != null)
{
    query = (from wv in query
             where (wv.TL == SearchSpec.TL)
             select wv);
}
...
return query.ToList();

...效果很好。 如果布尔值不为null，则使用它进行过滤，否则将忽略它。

现在，我必须过滤带有50个以上标志的某些数据，例如我的示例中的两个标志（AL，TL）。 我可以将if语句复制并粘贴50次，但这不是正确的方法...

我的想法是，使用一个大查询

var query = (from wv in Source select row); //Init query

query = (from wv in query
         where (SearchSpec.AL!=null && wv.AL==SearchSpec.AL)
         && (SearchSpec.TL!=null && wv.TL==SearchSpec.TL)
         ...
         select wv);

这似乎更好，但是仍然可以复制粘贴。

直截了当：有一种方法可以动态生成这些语句，例如通过使用反射来获取bool?类型的所有Properties bool? 然后...嗯，这是我的问题。

Answer 1

你想要那样的东西吗？

    var query = (from wv in Source select row); //Init query

    query = (from wv in query
                 select wv);

    query = CreateDynamicBoolFilter(SearchSpec, query);

    public static IEnumerable<Source> CreateDynamicBoolFilter(SearchSpec searchSpec, IEnumerable<Source> query)
    {
        //Firstly, bool? properties of searchSpech object are retrieved using reflection
        var booleanProperties = searchSpec.GetType()
                .GetProperties()
                .Where(prop => prop.PropertyType == typeof(bool?));

        foreach (var prop in booleanProperties)
        {
            var propValue = (bool?) prop.GetValue(searchSpec, null);
            if (propValue != null) // Determine to prop value is nullable, if it doesn't apply filter
            {
                var propName = prop.Name;
                query = query.Where(x => (bool?) x.GetType().GetProperties().FirstOrDefault(p => p.Name == propName)?.GetValue(x, null) == propValue);
            }
        }
        return query;
    }