本文介绍了防止实体框架中的联合排序结果的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

在SQL Server union 中,结果基于主键列进行排序。我想在实体框架中防止这种行为。

在中,@ praveen解释了如何在纯SQL中做到这一点。但是我想在实体框架中执行此操作。

我的代码

In SQL server union, result is sorted based on primary key column. I want to prevent this behavior in entity framework.
In this post, @praveen has explained how to do this in pure sql. But I want to do this in entity framework.
My code:

public virtual ActionResult Search(string keyword)
{
    var products = _db.Products
        .Where(x => x.IsActive)
        .AsQueryable();

    var productExactlyTitle = products.Where(x => x.Title == keyword);
    var productStartTitle = products.Where(x => x.Title.StartsWith(keyword));
    var productContainsTitle = products.Where(x => x.Title.Contains(keyword)
                                                   || x.Title.Contains(keyword)
                                                   || x.SubTitle.Contains(keyword)
                                                   || x.OtherName.Contains(keyword));


    var productList = productExactlyTitle.Union(productStartTitle)
        .Union(productContainsTitle)
        .Take(10)
        .AsEnumerable()
        .Select(x => new ProductItemViewModel()
        {
            Id = x.Id,
            Title = x.Title,
            Price = x.Price.ToPrice(),
            Image = x.Images.FirstOrDefault(y => y.IsCoverPhoto)?.ImageUrl
        });

        // some code ...
}

I想要显示具有以下顺序的记录:

I want to show records with below order:

第一: productExactlyTitle的记录

第二: productStartTitle的记录

第三: productContainsTitle 的记录

但是结果按 Id排序列!

有办法吗?

推荐答案

在SQL中,所有未明确设置 order 的查询都被认为是无顺序的。 (并且EF查询翻译成SQL)。因此,如果您要在联合后指定特定的订单,则只需指定它即可。

In SQL all queries without an order by explicitly set is considered unordered. (and EF queries a translated into SQL). So if you want a specific order after your union just specify it.

var result = q1.Union(q2).OrderBy(x => x.?);

对于您的特定情况:

var p1 = productExactlyTitle.Select(x => new { Item = x, Order = 1 });
var p2 = productStartTitle.Select(x => new { Item = x, Order = 2 });
var p3 = productContainsTitle.Select(x => new { Item = x, Order = 3 });
var productList = p1.Union(p2)
                    .Union(p3)
                    .OrderBy(x => x.Order)
                    .Select(x => x.Item)
                    .Take(10);

这篇关于防止实体框架中的联合排序结果的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

09-05 03:09