实体框架4-连接2个表然后对其进行分页的语法是什么? [英] Entity Framework 4 - What is the syntax for joining 2 tables then paging them?

问题描述

我有以下带有2个联接表的linq-to-entities查询，我想向其中添加分页:

I have the following linq-to-entities query with 2 joined tables that I would like to add pagination to:

IQueryable<ProductInventory> data = from inventory in objContext.ProductInventory
    join variant in objContext.Variants
        on inventory.VariantId equals variant.id
     where inventory.ProductId == productId
     where inventory.StoreId == storeId
     orderby variant.SortOrder
     select inventory;

我意识到我需要使用.Join()扩展方法，然后调用.OrderBy().Skip().Take()来执行此操作，我只是迷上了Join()的语法，并且可以似乎找不到任何示例(在线或书籍中).

I realize I need to use the .Join() extension method and then call .OrderBy().Skip().Take() to do this, I am just gettting tripped up on the syntax of Join() and can't seem to find any examples (either online or in books).

注意::我加入表格的原因是为了进行排序.如果有一种比关联表更好的基于相关表中的值进行排序的方法，请将其包括在您的答案中.

NOTE: The reason I am joining the tables is to do the sorting. If there is a better way to sort based on a value in a related table than join, please include it in your answer.

2种可能的解决方案

我想这只是一个可读性问题，但是这两个都可以工作并且在语义上是相同的.

I guess this one is just a matter of readability, but both of these will work and are semantically identical.

IQueryable<ProductInventory> data = objContext.ProductInventory
                .Where(y => y.ProductId == productId)
                .Where(y => y.StoreId == storeId)
                .Join(objContext.Variants,
                    pi => pi.VariantId,
                    v => v.id,
                    (pi, v) => new { Inventory = pi, Variant = v })
                .OrderBy(y => y.Variant.SortOrder)
                .Skip(skip)
                .Take(take)
                .Select(x => x.Inventory);

2

var query = from inventory in objContext.ProductInventory
    where inventory.ProductId == productId
    where inventory.StoreId == storeId
    join variant in objContext.Variants
        on inventory.VariantId equals variant.id
    orderby variant.SortOrder
    select inventory;

var paged = query.Skip(skip).Take(take);

对Khumesh和Pravin的帮助表示感谢.感谢其余的贡献.

Kudos to Khumesh and Pravin for helping with this. Thanks to the rest for contributing.

推荐答案

在查询中添加以下行

var pagedQuery = data.Skip(PageIndex * PageSize).Take(PageSize); 

数据变量是IQueryable，因此您可以添加add skip&采取方法.并且如果您在Product&变体，您实际上并不需要显式加入，您可以引用类似这样的变体

The data variable is IQueryable, so you can put add skip & take method on it. And if you have relationship between Product & Variant, you donot really require to have join explicitly, you can refer the variant something like this

IQueryable<ProductInventory> data = 
             from inventory in objContext.ProductInventory
             where inventory.ProductId == productId && inventory.StoreId == storeId
             orderby inventory.variant.SortOrder
             select new()
             {
                 property1 = inventory.Variant.VariantId,
                 //rest of the properties go here
             }
pagedQuery = data.Skip(PageIndex * PageSize).Take(PageSize); 

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