linq 动态判断

以前要不是使用扩展方法

要么使用如(t2&&判断条件)||（s1&&判断条件）

其实可以简单的实现扩展一个whereIf即可（abp实现），如下所示

···

///

/// Filters a by given predicate if given condition is true.

///

/// Queryable to apply filtering

/// A boolean value

/// Predicate to filter the query

/// Filtered or not filtered query based on

public static IQueryable WhereIf(this IQueryable query, bool condition, Expression<Func<T, bool>> predicate)

{

return condition

? query.Where(predicate)

: query;

}

    /// <summary>
    /// Filters a <see cref="IQueryable{T}"/> by given predicate if given condition is true.
    /// </summary>
    /// <param name="query">Queryable to apply filtering</param>
    /// <param name="condition">A boolean value</param>
    /// <param name="predicate">Predicate to filter the query</param>
    /// <returns>Filtered or not filtered query based on <paramref name="condition"/></returns>
    public static IQueryable<T> WhereIf<T>(this IQueryable<T> query, bool condition, Expression<Func<T, int, bool>> predicate)
    {
        return condition
            ? query.Where(predicate)
            : query;
    }

···

使用

例如：

var query = _taskRepository.GetAll().Include(t => t.AssignedPerson)

.WhereIf(input.State.HasValue, t => t.State == input.State.Value)

.WhereIf(!input.Filter.IsNullOrEmpty(), t => t.Title.Contains(input.Filter))

.WhereIf(input.AssignedPersonId.HasValue, t => t.AssignedPersonId == input.AssignedPersonId.Value);