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.
The method receives:
public TEntity Get(object id, params Expression<Func<TEntity, object>>[] includedRelatedEntities)
{
return GetById(IncludeEntities(DBContext.Set<TEntity>().AsQueryable(), includedRelatedEntities), id);
}
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>>)
An example of use is the following one:
var master = MasterRepository.Get(1, x => x.BranchOffice.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.
From one to many relationships, it works fine, but for related lists, I dont know how to resolve it using an expression.
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);
Details is a list, so I cant access product as it is in the example above.
How can I express that in a Expression<Func<TEntity, object>>?
EDIT:
I´ve already tried:
var master = MasterRepository.Get(1, x => x.Details.Select(y=> y.Product));
But I´m getting the following exception:
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.'
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.
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;
}
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.
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();
I hope it will helps you.
