Is there a way to get entity objects to automatically pull all relevant data through the relationships instead of having having to .Include everything I want populated? I can't use lazy loading as this needs to be serialized to go over WCF. It would just be fantastic to have it auto populate the relevant collections.
No there is no build in feature which will automatically eagear load whole object graph. You must always explicitly say which navigation properties you want to eager load (by using Include method or LoadProperty method).
Edit:
Based on your comment: Generally it should be possible to build some auto loader - but it will not be easy. ObjectContext has MetadataWorkspace property which contains all metadata about your entities. You can load all information about your entities from metadata and add needed inclueds to the query. I expect one problem - you must somehow handle cyclic references. If you need some example how to extract information about entities check T4 POCO generation template.
I came across this querstion recently because I was looking for something similar.
Since EF Core 6 there is a AutoInclude method that configures whether a navigation should be included automatically.
This can be done in the OnModelCreation method in the DbContext class:
modelBuilder.Entity<Theme>().Navigation(e => e.ColorScheme).AutoInclude();
This would load the ColorScheme for every Theme when running the query:
var themes = context.Themes.ToList();
See Model configuration for auto-including navigations
Related
What are the possibilities to avoid circular reference with Entity Framework 6 during JSON serialization with ASP.NET Web API?
I generated a edmx (Entity Data Model) file for Entity Framework 6, database first. I try to build an API with ASP.NET Web API. When I try to return my JSON object in my controllers I get a runtime exception of serialization because of circular reference.
Indeed when I double check my database and my entities I see one of my entity contains a list another entity that contain a list of my previous entity. let say I have a book entity that contains authors and each author entity contains a list of books. This is something common with relative database but impossible to resolve in JSON serialization (or impossible to resolve for the .NET serializer).
I don't want to change my database but I'm ready to break the wrong list into my entities or edmx file. What can I do?
What I have tried:
I already tried the solution that consist of creating new models or entities and using a mapping tool (http://www.codeproject.com/Articles/292970/Avoiding-Circular-Reference-for-Entity-in-JSON-Ser or the solution explained by by Shawn Wildermuth on Pluralsight).
This solution sounds more like a workaround than a real solution. It should exist something in edmx file or in Entity Framework to tell the JSON serializer what can cause circular reference, what can and must be serialized and what cannot be serialized, right?
There is technically no problem to serialize the domain model directly. To avoid circular reference you cannot use lazy loading. You must keep control of the loading. To do so
remove the virtual before each collection of your model (in code first approach)
set lazy loading configuration to false (in database first approach)
Don't try to serialize your domain model directly. Create a view model that returns the data in the exact format you want. Use you domain model to populate the view model. Much more information here Why do we use ViewModels?
You need to have a ViewModel that will act as the interface between your UI and your backend data structure.
Backend data structure is designed to be easilly stored and retrieved to and from the database. So by writing some ViewModel "adapters" you are not violating the "don't repeat yourself" rule.
Hope it helps.
I had to solve the same problem today. The easiest and the clear way for me was to remove the Navigation property from one of the entities on the entity model.
Open your model.edmx and remove the unwanted Navigation property which is causing the circular reference. In your case
Book references Author. so book entity model has Author navigation property.
If you do not want Author to reference Book, just remove Book navigation property from Author data model on the edmx file. So, there is only one way referencing.
I'm using AutoMapper as an ORM in application with Entity Framework v6.
My problem statement is that if I executes a single query via LINQ to Entities on any single entity and maps entity data via AutoMapper with DTO, many other queries will be executed at the same time while data binding.
Kindly anyone let me know, how to avoid this problem.
This is expected behavior. Remember, AutoMapper just looks at the destination type and will map matching properties from the source type. If you don't want some properties to be mapped lazily, you have several options:
Remove the properties from the destination model
Use Include to eagerly fetch properties
Use LINQ projection in AutoMapper (ProjectTo) to force EF to use the Select LINQ projection to grab whatever data it needs to based on the source type
I think this may happens due to the lazy loading enabled.
Read this answer :
Is automapper preventing lazy loading with EF?
With EF 4.1, you used to remove the IncludeMetadataConvention in order to prevent EF from querying for database metadata on every query.
In EF 5, I get a warning about IncludeMetadataConvention being obsolete, and in LinqPad, I can see that EF is now querying for migration history on every use. I'm working on a database first project (but using POCO's and DbContext). I don't want the overhead of these extra queries. How do I turn them off?
Update
I found that I can disable this on a per-dbContext basis by calling
System.Data.Entity.Database.SetInitializer<theDbContext>(null);
However, I would like to be able to disable initialization globally (Imagine a large app, and we want to ensure that we are not running these queries (and definitely not trying to create a database) when it is deployed for production.
If you need to do it for every context type in your large application you can create some code which will go through all of your assemblies, find all types derived from DbContext and invoke that call through reflection for every found type.
Btw. since EF 4.3 you can also change initializer from configuration but it is still per context basis because people usually don't have more than one.
Why not put the code in the constructor of your DbContext classes?
I do this as well as set a parameter to disable AutoDetectChangesEnabled, LazyLoading & Proxy CreationEnabled.
there has been quite bit of discussion on this topic ( Modifying an Entity Framework Model at Run-Time), but so far I haven't been able to find a nice solution to the problem. We currently have a model built with EF 4.0 and need to allow customers to add custom fields to various tables. We have currently solved the problem with a few generic tables that describe the new properties, but we're finding that the solution is not performing well.
Does anyone know of a good way to dynamically add columns to the database and also update the ORM to reflect that at run-time?
There is no good, nice or manageable way to update EF at runtime to reflect changes in the database. If you really have a database which must change at runtime EF is not good tool for you. EF is strongly typed - every change to database must be reflected not only in mapping but also in entity classes used for loading and persisting data.
Changing entity classes at runtime always goes to area of emitting IL code at runtime. If you pass the process of creating dynamic assembly with dynamic module and dynamic entity types you will face a lot of new challenges:
You will not change your existing types - you will generate a new type every time the user adds or removes some property.
A new type generation brings a new performance cost for rebuilding context's metadata workspace. You must also make sure that this is correctly synchronized if you use it on a server. Another problem is that all existing instances of the old type (before adding or removing property) are now unknown to new instances of EF context and cannot be persisted. If you want to persist them as well you need EF context instances with old metadata workspace as well.
A lot of your code will probably use dynamic instead of real type = no compile time checking. Inheritance and interfaces will not be useful when interacting directly with EF because inheritance must be mapped (you don't want it) and interfaces are not accepted by EF.
The new type is unknown at design time - you cannot use it for design time code and compilation.
EF doesn't like dynamic or ExpandoObject because it uses reflection for mapping -> at runtime your dynamic instance must be correct type otherwise reflection will not work.
How to write queries for dynamic type? The query always starts at generic instance of DbSet or ObjectSet created for concrete type - you must be able to make those instances dynamically as well. Generic argument must be a type mapped to current context - dynamic will not help in this case because it is not a mapped type.
.NET has a nice behavior for this case. It cannot unload assembly. So every time you generate a new type you will have an old time loaded as well.
Do you still want to change EF at runtime? Your current approach is correct one. Simply tune it for better performance but beware that these requirements always come with performance costs - especially with EF.
Alternatively use the last approach mentioned with linked table - fixed number of predefined custom fields directly in the main entity.
I have an application which uses Entity Framework Code First. I am attempting to write my resource access layer. I have several objects which all have separate database tables and a lot of object relationships. Can someone point me to an up-to-date example of CRUD methods with related objects? Everything I have found uses an older version (I use DbContext, not ObjectContext, etc.) and I am having problems writing it myself.
For example, I am currently working on an object with a parent-child relationship with itself. I am attempting to write the Create method. If I use context.Objects.Add(newObject) then all the children objects also have their state changed to Added, which means that duplicate children are added. So I tried looping through all the children and attaching them to the context, but then any children that did not previously exist do not get added to the database and a DbUpdateException is thrown.
Is there a generic way I can attach all related entities and have their states be correct? Any help you can give me would be appreciated. Thanks!
Edit:
I tried explicitly loading the children using Load() and then adding the initial object. Unfortunately, it caused an exception because the parent comment had the child in its list of children but the parentID of the existing child had not yet been updated.
No there is no way to attach whole graph and let EF automatically set correct state - these problems didn't changed since ObjectContext API. You must always set state manually for each entity and relation or you must build the graph from attached entities. The only exception are Self tracking entities but they are not supported with DbContext API.