EF1：使用 .OfType<> 过滤实体类的派生类型通过传递字符串值

发布于 10-12 23:40 字数 1141 浏览 13 评论 0 原文

我遇到了一种情况，我试图使用派生子类来过滤 LINQ 选择。

ctx.BaseEntity.OfType() - 这工作正常。

不过，我想使用字符串值来完成此操作。当我有很多（> 20）子类并且不使用 OfType 选择实体时，我遇到了性能障碍。我有一个从基类呈现的通用 UI，因此我不知道在编译时将返回什么类类型。

所以我想做的是：

执行投影选择我所在的位置仅返回子类类型数据库

执行第二次选择使用该值作为 OfType 来只选择相关的相关数据库中的实体（无质量生成工会）

 int id = 1;
    var classType = (来自 ctx.BaseClass.Include("ClassType") 中的 c)
                               其中 c.id == id
                               选择新的
                                          {
                                              c.ClassType.TypeName
                                          }）。第一的（）;

    BaseClass caseQuery = ctx.BaseClass.OfType()
                    .include("类类型")
                    .include("ChildEntity1")
                    .include("ChildEntity2")
                    .Where(x => x.id== id);

但显然这不起作用，因为 OfType 需要类型而不是字符串

关于如何实现这一目标有什么想法吗？

更新： 作为原始问题的旁注，事实证明，当您项目使用导航属性的查询时，它也会构建怪物 SQL，因此我最终使用存储过程从 BaseClass 填充我的 ClassType 实体ID。

原文

I have a situation where I'm trying to filter a LINQ select using a derived sub class.

ctx.BaseEntity.OfType<SubClass>() - this works fine.

However I'd like to do this using a string value instead. I've come across a performance barrier when I have lots (>20) Sub Classes and selecting an Entity without using OfType just isn't an option. I have a generic UI that renders from the base class, so I don't know what Class Type will be returned at compile time.

So what I'd like to do is this:

Perform a projected Select where I
return just the SubClassType from
the database

Perform a second select
using this value as the OfType to
only select the relevant related
entity from the database (No mass
unions generated)

    int id = 1;
    var classType = (from c in ctx.BaseClass.Include("ClassType")
                               where c.id == id
                               select new
                                          {
                                              c.ClassType.TypeName
                                          }).First();

    BaseClass caseQuery = ctx.BaseClass.OfType<classType.TypeName>()
                    .Include("ClassType")
                    .Include("ChildEntity1")
                    .Include("ChildEntity2")
                    .Where(x => x.id== id);

But obviously this won't work because OfType requires a Type and not a string.

Any ideas on how I can achieve this?

Update:
As a side note to the original question, it turns out that the moment you project a query that uses a Navigation Property - it builds the monster SQL too, so I've ended up using a stored procedure to populate my ClassType entity from the BaseClass Id.

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与风相奔跑 2024-10-19 23:40:18

所以我刚刚使用 eSQL 让它工作，而我以前从未使用过它。我在这里发布了代码，以防它对某人有帮助。还有其他人有他们能想到的更强类型的解决方案吗？

BaseClass caseQuery = ctx.BaseClass.CreateQuery<BaseClass>("SELECT VALUE c FROM OFTYPE(Entities.[BaseClass],namespace.[" + classType.TypeName + "])  as c")
                .Include("ClassType")
                .Include("ChildEntity1")
                .Include("ChildEntity2")
                .Where(x => x.id== id).FirstOrDefault();

So I've just got it to work using eSQL, which I'd never used before. I've posted the code here just in case it helps someone. Has anyone else got a more strongly typed solution they can think of?

BaseClass caseQuery = ctx.BaseClass.CreateQuery<BaseClass>("SELECT VALUE c FROM OFTYPE(Entities.[BaseClass],namespace.[" + classType.TypeName + "])  as c")
                .Include("ClassType")
                .Include("ChildEntity1")
                .Include("ChildEntity2")
                .Where(x => x.id== id).FirstOrDefault();

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相思故 2024-10-19 23:40:18

要回答有关使用字符串/运行时类型调用 OfType 的标题问题，您可以执行以下操作：

// Get the type, assuming the derived type is defined in the same assembly 
// as the base class and you have the type name as a string
var typeToFilter = typeof(BaseClass)
     .Assembly
     .GetType("Namespace." + derivedTypeName);

// The use reflection to get the OfType method and call it directly
MethodInfo ofType = typeof(Queryable).GetMethod("OfType");
MethodInfo ofTypeGeneric = method.MakeGenericMethod(new Type[] { typeToFilter });
var result = (IQueryable<Equipment>)generic.Invoke(null, new object[] { equipment });

将其与存储过程结合起来以获取类名，并且您（应该？）避免大量连接 -我没有每个类型的表实现可供使用，所以我无法测试。

To answer the headline question about calling OfType with a string / runtime type, you can do the following:

// Get the type, assuming the derived type is defined in the same assembly 
// as the base class and you have the type name as a string
var typeToFilter = typeof(BaseClass)
     .Assembly
     .GetType("Namespace." + derivedTypeName);

// The use reflection to get the OfType method and call it directly
MethodInfo ofType = typeof(Queryable).GetMethod("OfType");
MethodInfo ofTypeGeneric = method.MakeGenericMethod(new Type[] { typeToFilter });
var result = (IQueryable<Equipment>)generic.Invoke(null, new object[] { equipment });

Combine this with your stored procedure to get the class name and you (should?) avoid the massive join - I don't have table-per-type implementation to play with so I can't test.

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