访问表达式树中与子级(列表)相关的属性 [英] Access children(list) related property in Expression tree
问题描述
我为我的实体Master
创建了一个存储库.在存储库中,我有一个Get
方法来使用实体核心通过ID获取我的实体.
I created a repository for my entity Master
. In the repository, I have a Get
method to get my entity by Id using Entity Core.
该方法收到:
public TEntity Get(object id, params Expression<Func<TEntity, object>>[] includedRelatedEntities)
{
return GetById(IncludeEntities(DBContext.Set<TEntity>().AsQueryable(), includedRelatedEntities), id);
}
然后,当我在代码中使用它时,我只是将要查找的实体的ID以及需要包含在查询中的相关实体的表达式树(Expression<Func<TEntity, object>>
)传递给该方法
Then, when I use it in my code, I just pass to the method the id of the entity I´m looking for and and expression tree of the related entities that I need to include in the query (Expression<Func<TEntity, object>>
)
使用示例如下:
var master = MasterRepository.Get(1, x => x.BranchOffice.Location);
在这种情况下,我正在寻找ID = 1的Master,并且希望它包含与BranchOffice
相关的实体和与该BranchOffice
相关的Location
.
In that case I´m looking for the Master with Id = 1 and I want it to include the BranchOffice
related entity and the Location
related to that BranchOffice
.
从一个到多个关系,它都能正常工作,但是对于相关列表,我不知道如何使用表达式来解决它.
From one to many relationships, it works fine, but for related lists, I dont know how to resolve it using an expression.
例如,如果我想包含与我的Master
相关的名为Details
的Detail
列表中的Product
实体,我不知道如何在表达式树中表达它.
For example, if I want to include the Product
entity of the list of Detail
named Details
related to my Master
, I dont know how to express it in the expression tree.
var master = MasterRepository.Get(1, x => x.Details.Product);
详细信息是一个列表,因此我无法访问上面的示例中的产品.
Details is a list, so I cant access product as it is in the example above.
如何在Expression<Func<TEntity, object>>
中表达出来?
How can I express that in a Expression<Func<TEntity, object>>
?
我已经尝试过:
var master = MasterRepository.Get(1, x => x.Details.Select(y=> y.Product));
但是我遇到以下异常:
属性表达式'x => {来自[x]中的详细信息y.详细信息选择 [y] .Product}'无效.表达式应表示一个属性 访问:"t => t.MyProperty".有关包括相关内容的更多信息 数据,请参阅go.microsoft.com/fwlink/?LinkID=746393.'
The property expression 'x => {from Detail y in [x].Details select [y].Product}' is not valid. The expression should represent a property access: 't => t.MyProperty'. For more information on including related data, see go.microsoft.com/fwlink/?LinkID=746393.'
推荐答案
我不知道您可以更改或替换IncludeEntities
实现,因此答案可能对您没有帮助.好吧, EF.Core 中的x => x.Details.Product
看起来像这样DbContext.Set<SomeType>().Include(x => x.Details).ThenInclude(o => o.Product)
.
I don't know can you change or replace IncludeEntities
implementations, so maybe answer would not be helpful for you. Well, x => x.Details.Product
will looks like this DbContext.Set<SomeType>().Include(x => x.Details).ThenInclude(o => o.Product)
in the EF.Core.
因此,如果要包括多个级别,建议您在运行时构建一个包含Include
和ThenInclude
的查询.因此,该查询将从输入表达式中构建,如下所示:x => x.Details.Select(y => y.Product)
.生成此查询的方法是
So if you want to include multiple levels I can suggest you to build a query at runtime that will contains Include
and ThenInclude
. So, this query will be built from input expression looks like this x => x.Details.Select(y => y.Product)
. It's method that build this query:
/// <summary>
/// Takes include looks like 'x => x.Collections.Select(o => o.List.Select(p => p.Date))'
/// </summary>
public static IQueryable<T> GetQueryWithIncludes<T>(IQueryable<T> query, Expression<Func<T, object>> arg)
{
// Tiny optimization
ParameterInfo[] parameters;
var includeInfo = typeof(EntityFrameworkQueryableExtensions).GetMethods().Where(info => info.Name == "Include" &&
(parameters = info.GetParameters()).Length == 2 &&
typeof(Expression).IsAssignableFrom(parameters[1].ParameterType)).Single();
// Retrieve then include that take first param as 'IIncludableQueryable<TEntity, ICollection<TPreviousProperty>>'
var thenIncludeInfo = typeof(EntityFrameworkQueryableExtensions).GetMethods().Where(info => info.Name == "ThenInclude").ToList()[1];
// Retrieve then include that take first param as 'IIncludableQueryable<TEntity, IEnumerable<TPreviousProperty>>'
var lastThenIncludeInfo = typeof(EntityFrameworkQueryableExtensions).GetMethods().Where(info => info.Name == "ThenInclude").ToList()[0];
// Retrieve all selection from input expression
var lambda = arg as LambdaExpression;
var method = arg.Body as MethodCallExpression;
var result = new List<Expression>();
while (method != null)
{
result.Add(Expression.Lambda(method.Arguments[0], lambda.Parameters[0]));
lambda = method.Arguments[1] as LambdaExpression;
method = lambda.Body as MethodCallExpression;
}
result.Add(lambda);
// Add Include and ThenInclude to IQueryable
for (int i = 0; i < result.Count; ++i)
{
var lambdaExp = result[i] as LambdaExpression;
query = i == 0
? includeInfo.MakeGenericMethod(lambdaExp.Parameters[0].Type, lambdaExp.ReturnType).Invoke(null, new object[] { query, lambdaExp }) as IQueryable<T>
: i == result.Count - 1
? lastThenIncludeInfo.MakeGenericMethod((result[0] as LambdaExpression).Parameters[0].Type, lambdaExp.Parameters[0].Type, lambdaExp.ReturnType).Invoke(null, new object[] { query, lambdaExp }) as IQueryable<T>
: thenIncludeInfo.MakeGenericMethod((result[0] as LambdaExpression).Parameters[0].Type, lambdaExp.Parameters[0].Type, lambdaExp.ReturnType).Invoke(null, new object[] { query, lambdaExp }) as IQueryable<T>;
}
return query;
}
顺便说一句,方法采用一个表达式,但是可以对其进行少量修改,因此它将采用表达式数组,或者您可以从循环中直接为所有表达式调用该方法.
By the way, method takes a one expression, but it can be lightly modified, so it will takes array of expression or you can directly invoke the method from a loop for all of expressions.
下面的代码仅是用法.我写了一个树形的小类进行测试:
Code below is just usage. I wrote a tree small classes for testing:
public class Test
{
public int Id { get; set; }
public DateTime TestDate { get; set; }
public ICollection<Level> Levels { get; set; }
}
public class Level
{
public int Id { get; set; }
public ICollection<LevelDetail> LevelDetails { get; set; }
}
public class LevelDetail
{
public int Id { get; set; }
public DateTime LevelDate { get; set; }
}
...
// These results are the same and have the same expression trees
var resultByInclude = context.Tests
.Include(o => o.Levels)
.ThenInclude(p => p.LevelDetails).ToList();
var resultBySelect = GetQueryWithIncludes(context.Tests,
o => o.Levels.Select(p => p.LevelDetails)).ToList();
我希望它将对您有帮助.
I hope it will helps you.
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