Category: Entity framework filter child collection

Entity framework filter child collection

Suppose I have a model with Customer and Order objects. Obviously, each Order belongs to exactly one Customer, and each Customer can have zero or more Order entities. How do I do this? It seems such a simple obvious requirement, which would be pretty simple in SQL. I originally wanted to return a collection of Customer objects, as this is easier to work with, but this is as close as I coudl get. I think I got what your mean from the description.

Orders is a collection, so you should c. OldDate as your where condition, like this way:. Please try this code, If you have any questions, please feel free to let me know. I looked at Anybut got the impression that it was doing something slightly different maybe i didn't phrase my question clearly enough.

If I understand right, Any will mean that the query will include all customers who have an order this year, but the Orders collection will include all of their orders, including ones not from this year.

That's not what I want. I want customers who have ordered this year, and only those orders from this year. So if customer A has placed one order this year, and two last year, the query would return customer A with just the one order from this year.

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Yes, you are right, Any will query all customer's orders, and this query clause just returns the customer who has any orders which OrderDate in this year in Order collection. When your get Orders, the all Orders will be shown, EF will not help you get the filter records. If you want to get the Customers and orders in one query, you may use Anonymous class like this way:. Customers where c. By the way, what's your aim to query in this way?

Edit: I realised afterwards that this does NOT answer my question. See my subsequent post lower down. I found the answer to my question, and it turned out to be really simple - once you know Linq! The following is what I wanted Obviously, my full query is a little more complex, but the point I was struggling with was how to get a collection of Order objects with each customer, where the orders were only from this year.

The above query seems to do the trick, and doesn't require an anonymous type. Having played with this some more, I realised that the query I posted does not do what I wanted. That query which has now been messed up by the lousy editor on these forums did the equivalent of an SQL outer join, meaning that it returned one row for each order.

Thus if customer Fred had two orders this year, there would be two rows in the results set, both with customer Fred, and one for each order.

entity framework filter child collection

What I want is to have one row for each customer, and a have in that row a collection of orders. So Fred would appear in just one row, and the collection would have two orders in it. Just noticed this last part of your post.

Firstly, thanks for posting the link.Here is sample model which to configure. It has root entity - Order and collection of OrderItems. With this model in place I want an Order to be responsible for child collection - when I save Order also OrderItems should be saved, when I remove item from collection and save Orderremoved item should be deleted in database.

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But when you remove item from collection it just removes relationship between Order and OrderItem. Now OrderId column is automatically generated in database and we do not have it in our model. So first of all we have to add OrderId to OrderItem. Now we have to configure composite key. It is easy with Data Annotationsbut I do not want my model to depend on Entity Framework directly.

So I will do it using fluent API. Next define composite key for OrderItem using anonymous object. Also configure Id column values to be auto-generated by database, because it does not generate those for composite keys. If instead you assign new collection, it will not remove items and leaves them. In this article I am showing how to configure it to handle entity's child collections that those properly gets added and removed from collection.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Can someone clarify if I am right in thinking that I can't get a parent and a subset of it's children from the db?

Children collection, all children will be present not just those over 5 years old. Now the query does make sense to me I've asked to include children and I've got them!

I have found a few blogs and SO posts that touch on the subject, but nothing that explains it well enough for my little brain. Having read this blog thanks Daz Lewis I still don't get it!!!

In the example given in the blog, I can see how I can achieve it against a single instance of Parent, but I'm struggling to work out how I can do it with a collection.

In answer to DonAndre's comment, I am after a A list of parents who have a child older than 5 and include only those children. The only way to get a collection of parents with a filtered children collection in a single database roundtrip is using a projection.

It is not possible to use eager loading Include because it doesn't support filtering, Include always loads the whole collection. The explicite loading way shown by Daz requires one roundtrip per parent entity. You can directly work with this collection of anonymous type objects. You can also project into your own named type instead of an anonymous projection but not into an entity like Parent. EF's context will also populate the Children collection of the Parent automatically if you don't disable change tracking using AsNoTracking for example.

In this case you can then project the parent out of the anonymous result type happens in memory, no DB query :. Children will contain your filtered children for each Parent.

I am after a A list of parents who have a child older than 5 and include only those children. Taking your example the following should do what you need. Take a look here for more info. I think parents and child are not really well suited as separate entities.

A child can always also be a parent and usually a child has two parents a father and a motherso it's not the simplest context. But I assume you just have a simple 1:n relationship as in the following master-slave model that I used. What you need to do is make a left outer join that answer has led me on the right path.

Such a join is a bit tricky to do, but here's the code. Note that it is important to perform the additional where clause on the age on the joined collection and not between the from and the select.

Note that I used an anonymous type to store the hierarchical result. You can of course create also a specific type like this. That makes it easier if you need to pass these results to other methods. Learn more.Here you will learn how to load related entities in an entity graph explicitly. Even with lazy loading disabled in EF 6it is still possible to lazily load related entities, but it must be done with an explicit call. Use the Load method to load related entities explicitly.

Consider the following example. In the above example, context. Entry student. Load loads the StudentAddress entity. The Reference method is used to get an object of the specified reference navigation property and the Load method loads it explicitly. In the same way, context. Load loads the collection navigation property Courses of the Student entity. The Collection method gets an object that represents the collection navigation property.

The Load method executes the SQL query in the database to get the data and fill up the specified reference or collection property in the memory, as shown below. The Query method enables us to write further LINQ queries for the related entities to filter out related data. In the above example. Query allows us to write further queries for the StudentCourses entity. Entity Framework Courses on Pluralsight.Entity Framework supports three ways to load related data - eager loading, lazy loading and explicit loading.

The techniques shown in this topic apply equally to models created with Code First and the EF Designer. Eager loading is the process whereby a query for one type of entity also loads related entities as part of the query. Eager loading is achieved by use of the Include method. For example, the queries below will load blogs and all the posts related to each blog. Include is an extension method in the System.

Entity namespace so make sure you are using that namespace. It is also possible to eagerly load multiple levels of related entities. The queries below show examples of how to do this for both collection and reference navigation properties. It is not currently possible to filter which related entities are loaded.

Include will always bring in all related entities. When using POCO entity types, lazy loading is achieved by creating instances of derived proxy types and then overriding virtual properties to add the loading hook. For example, when using the Blog entity class defined below, the related Posts will be loaded the first time the Posts navigation property is accessed:. Most serializers work by accessing each property on an instance of a type.

Property access triggers lazy loading, so more entities get serialized. On those entities properties are accessed, and even more entities are loaded. The following sections show how to do this. Loading of the Posts collection can still be achieved using eager loading see Eagerly Loading above or the Load method see Explicitly Loading below.

Lazy loading can be turned off for all entities in the context by setting a flag on the Configuration property. For example:. Loading of related entities can still be achieved using eager loading see Eagerly Loading above or the Load method see Explicitly Loading below. Even with lazy loading disabled it is still possible to lazily load related entities, but it must be done with an explicit call.

The Reference method should be used when an entity has a navigation property to another single entity. On the other hand, the Collection method should be used when an entity has a navigation property to a collection of other entities.

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The Query method provides access to the underlying query that Entity Framework will use when loading related entities. The Query method can be used with both reference and collection navigation properties but is most useful for collections where it can be used to load only part of the collection.

entity framework filter child collection

When using the Query method it is usually best to turn off lazy loading for the navigation property. This is because otherwise the entire collection may get loaded automatically by the lazy loading mechanism either before or after the filtered query has been executed.

entity framework filter child collection

While the relationship can be specified as a string instead of a lambda expression, the returned IQueryable is not generic when a string is used and so the Cast method is usually needed before anything useful can be done with it. Sometimes it is useful to know how many entities are related to another entity in the database without actually incurring the cost of loading all those entities.

You may also leave feedback directly on GitHub. Skip to main content. Exit focus mode. Eagerly Loading Eager loading is the process whereby a query for one type of entity also loads related entities as part of the query. NET Blog". Include "Posts".How do I go about ordering the teams by their name, and then have all the child members of each team sorted by their name?

It seems that do this I need to create a new DTO class and use a select. I'd like to use the EF entities already created, in this case Team has a navigation property to Members. Here is an example of filtering an Include but the same works for Ordering. You could dump your teams and their team members into an anonymous type probably not what you wantlike this:.

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How to order child collections of entities in EF entity-framework linq. There doesn't seem to be a neat way of ordering child collections in EF. Can anyone help? Bulk Delete. Bulk Update. Bulk Merge. Accepted Answer You could load the data and sort in memory after loading it. Name ; foreach var teamMember in team. Wouter de Kort.

Handling child collections in Entity Framework

Teams where t. I removed the 2nd solution, since it was pointed out that EF cannot select into entities. Ricky Smith. View more on Stack Overflow. Prime Library. Not affiliated with Stack Overflow.

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SaveChanges vs BulkSaveChanges. Try for free now.My main system entity is 'tagged' with a child collection of key value pairs, which I want to use to filter a listing of the main entities.

Entity Framework include filter child collection

However, the EF core query I've written below is far too slow for acceptable use. I'm a bit rusty with EF and using EF Core for the first timebut the problem is down to the way I'm filtering by the child Tag collection with the multiple.

Any commands the query performs perfectly when no Tag filters are specified. I can't think of a another way to filter the child Tag object collection against the selected Tag filter objects - a single filter Tag would be much simpler, and quicker, I imagine.

The only alternative I can currently think of is to do a custom SQL query myself, but it seems a shame to resort to that already when putting together my first EF Core query! The first thing to note is that your proposed query can't be evaluated fully as SQL because there's no SQL equivalent for a collection containing non-primitive values, tagSearchValues. This causes EF to auto-switch to client-side evaluation.

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That is, it pulls into memory all entities that meet the stuffFilter condition and all of their tags, and then it applies the tags predicate. That, evidently, is not efficient. Secondly, the query is inaccurate.

It requires a query that matches each combination, like this:. However, if you do that, EF will again turn to inefficient client-side evaluation and you'd even have to apply Include or lazy loading yourself to pull the tags into memory.

Moreover, for some reason, EF fires tons of redundant queries.

entity framework filter child collection

Fact of the matter is that EF like other ORMs isn't well-geared to such pair-wise comparisons server-side. Therefore you need a predicate builder to build the tag predicates. There are several predicate buiders, f. I use this one because it's nice and simple.

The recipe is: build a predicate and apply it in a Where :. I use Or because I assume from your query that you want entities having any tag in the search tags. That's why I start with a PredicateBuilder. True predicate, so the query will return results if there are no search tags, similar to your original query. EF Core has the unfortunate design property of silently executing queries on the client side if they can't be translated to SQL. EF Core - Filtering by a child collection of Key Value pairs extremely slow c entity-framework entity-framework-core linq-to-sql.

Question My main system entity is 'tagged' with a child collection of key value pairs, which I want to use to filter a listing of the main entities.

HasValue me. Bulk Delete. Bulk Update.


Author: Kazigis

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