冻结LINQ的IQueryable（作为了ToList（）。AsQueryable已（）会做）

问题描述

有没有办法冻结了的IQueryable 所以没有额外的连接访问数据库时，将添加到查询？例如，我可以做一个 .ToList（）冻结查询，但有性能影响，因为我做的任何过滤是中间层上，我没有从预过滤的性能提升数据库服务器

Is there a way to freeze an IQueryable so that no additional joins will be added to the query when hitting the database? For example, I could do a .ToList() to freeze the query, but that has performance impacts because any filtering I do is on the middle layer and I don't have any performance gains from pre-filtering on the db server?

修改为清楚起见上：

我有一个返回的IQueryable 客户端可以过滤/排序/按需要项目OData服务。我只是想阻止他们拉更多的数据出来。我能做到这一点做了ToList（）。AsQueryable已（），但失去了惰性加载的优势，有了它，可以让客户端过滤请求的全部目的

I have an OData service which returns an IQueryable that the client can filter/sort/project as needed. I just want to prevent them from pulling more data out. I could do that by doing ToList().AsQueryable(), but that loses the advantage of lazyLoading, and with it, the whole purpose of allowing the client to filter the request.

这是我看着一个方案是设置： EnableQueryAttribute.AllowedQueryOptions 排除展开，但即使我的初始查询有所扩大，客户端仍然选择那些部分预防。

One option that I looked at was to set: EnableQueryAttribute.AllowedQueryOptions to exclude Expand, however even if my initial Query had been expanded, the client is still prevented from selecting those parts.

推荐答案

林假设你确实有一个的IQueryable< T> ，而不是的IQueryable 。

如果你不想让你有客户端的所有访问的IQueryable< T> 方法，不返回的IQueryable< ; T> 。既然你想让他们只能够过滤器/排序/项目，创建一个对象巫婆包含的IQueryable< T> ，但只公开所需的方法和使用：

Im assuming that you actually have an IQueryable<T> instead of a IQueryable.

If you don't want your client having access to all IQueryable<T> methods, don't return an IQueryable<T>. Since you want them to be able to only filter/sort/project, create a object witch contains an IQueryable<T> but only expose the desired methods, and use that:

public interface IDataResult<T>
{
    IDataResult<T> FilterBy(Expression<Func<T, bool>> predicate);

    IDataResult<TResult> ProjectTo<TResult>(Expression<Func<T, TResult>> predicate);

    IDataResult<T> SortBy<TKey>(Expression<Func<T, TKey>> keySelector);

    IDataResult<T> SortByDescending<TKey>(Expression<Func<T, TKey>> keySelector);

    List<T> ToList();

    IEnumerable<T> AsEnumerable();
}

public class DataResult<T> : IDataResult<T>
{
    private IQueryable<T> Query { get; set; }

    public DataResult(IQueryable<T> originalQuery)
    {
        this.Query = originalQuery;
    }

    public IDataResult<T> FilterBy(Expression<Func<T, bool>> predicate)
    {
        return new DataResult<T>(this.Query.Where(predicate));
    }

    public IDataResult<T> SortBy<TKey>(Expression<Func<T, TKey>> keySelector)
    {
        return new DataResult<T>(this.Query.OrderBy(keySelector));
    }

    public IDataResult<T> SortByDescending<TKey>(Expression<Func<T, TKey>> keySelector)
    {
        return new DataResult<T>(this.Query.OrderByDescending(keySelector));
    }

    public IDataResult<TResult> ProjectTo<TResult>(Expression<Func<T, TResult>> predicate)
    {
        return new DataResult<TResult>(this.Query.Select(predicate));
    }

    public List<T> ToList()
    {
        return this.Query.ToList();
    }

    public IEnumerable<T> AsEnumerable()
    {
        return this.Query.AsEnumerable();
    }
} 

这样，你还可以防止EF和DB相关的依赖性您的应用程序攀升。 T> 方法将被包含的传播，而不是所有的地方这个类中，

That way you can also prevent EF and DB related dependencies creeping up on your application. Any change on IQueryable<T> methods will be contained within this class, instead of spread all over the place.

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