Dynamically query entities from Entity Framework for association to primary Entity

c# dynamic-queries entity-framework expression-trees reflection

Question

I know the title wasn't the greatest, but here is what I actually want to accomplish.

I have a details view that represents Entity1 and its associations. I am capturing the property names and values in a key/value pair. I am currently using reflection to set the Entity properties to the corresponding values for non associations. I doubt this is the most efficient way, but I have been unable to find a better way using Expression Trees. So now I need to set the associations of Entity1 to their corresponding entities based on the primary key of those entity associations, call them Entity2-4.

When iterating the Properties of Entity1, I don't know how to construct a dynamic query to Entity2-4 and set Entity1.association to the corresponding entity. Here is the code I have so far:

foreach (string k in e.Values.Keys)
{
    if (e.Values[k] != null && !String.IsNullOrEmpty(e.Values[k].ToString()))
    {
        System.Type objectType = Entity1.GetType();
        PropertyInfo[] p = objectType.GetProperties();

        foreach (PropertyInfo pi in p)
        {
            // set Entity1.Property for non associations (works just fine)
            if (pi.Name == k)
            {
                System.Type t = pi.PropertyType;
                pi.SetProperty(e.Values[k].ToString(), Entity1);
                break;
            }
            // when i see pi.Name contain Reference, I know I'm working on an association
            else if (pi.Name.Contains("Reference"))
            {
                // k is in the form of Entity.Property
                var name = pi.Name.Left("Reference");
                var keys = k.Split('.');
                var ent = keys[0];
                var prop = keys[1];
                if (name == ent)
                {
                    // here I need to obtain an instance from the db
                    // ie generate my dynamic query to the Entity with the name
                    // contained within the var "ent"

                    // I tried using reflection and could instantiate the entity 
                    // but it did me no good as I needed the entity from the db

                    var entityInstance = some dynamic query;

                    // here I need to set the association of Entity1 to entityInstance from above
                    // normally I would use reflection, but I'm not sure that would work
                    // since EntityReference is the actual property returned by reflection
                    Entity1.SetAssocation(prop, Entity2);
                    break;
                }
            }
        }
    }
}

EDIT

I basically need construct the entity and its association entities so that I can submit them to the data context. Entity 2 through 4 exist in the db, I need to query the db to obtain the instances to that I may associate them to the new Entity1 I am creating and going to submit.

My basic model:

Entity1

Entity1.ID
Entity1.Prop1
Entity1.Prop2
Entity1.Prop3
Entity1.Entity2
Entity1.Entity3
Entity1.Entity4

Entity2

Entity2.ID
Entity2.Name

Entity3

Entity3.ID
Entity3.Name

Entity4

Entity4.ID
Entity4.Name
1
1
4/10/2013 9:08:12 PM

Fastest Entity Framework Extensions

Bulk Insert
Bulk Delete
Bulk Update
Bulk Merge

Popular Answer

We've had an in-depth discussion about how to get the metadata out of the DbContext. Here are a few links to get you started. And I'll add some specific comments.

How I can read EF DbContext metadata programmatically?

A short summary (but you should check in there for more): 

using (var db = new MyDbContext())
{
    var objectContext = ((IObjectContextAdapter)db).ObjectContext;
    var container = objectContext.MetadataWorkspace.GetEntityContainer(objectContext.DefaultContainerName, DataSpace.CSpace);

    var dependents = ((EntitySet)(set)).ForeignKeyDependents;
    var principals = ((EntitySet)(set)).ForeignKeyPrincipals;
    var navigationProperties = ((EntityType)(set.ElementType)).NavigationProperties;

    // and e.g. for many-to-many (there is more for other types)
    ManyToManyReferences = navigationProperties.Where(np =>
        np.FromEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many &&
        np.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many)
        .Select(np => Extensions.CreateLambdaExpression<TEntity>(np.Name))
        .ToList();
}

@Goran Obradovic did a great job to wrap up what I started into a set of reusable queries (my due credits to him:).

I have worked out all other sorts of information that's in there. This is just for the DataSpace.CSpace (which is the most useful to you), but there is also DataSpace.SSpace etc. - which are more for creating SQL queries etc. I'll put most links at the bottom.

Specifics:
In your case following might be helpful:
(note: I'm not entirely sure what you're after, but I'm trying to guess here what's the direction that you're heading) 

db.Set<Worker>().Find(1);

Is the generic method for accessing DbSet for a specific entity.

You could also construct it from a Type if you need it to be fully dynamic, e.g....
(I always wanted to do this:)

MethodInfo setMethod = typeof(DbContext).GetMethod("Set", new Type[]{});
MethodInfo genericSetMethod = setMethod.MakeGenericMethod(new Type[] { typeof(YourEntity) });
var set = genericSetMethod.Invoke(db, new object[] {});

Put your entity - or your Type instead of typeof(YourEntity).

You could then proceed and query that for e.g. Find(id) - for that entity - to get concrete values etc.

That's as dynamic as it gets - I'm not sure if that's what you want - but I'm just throwing things out here in case you need it.

That should get you started at least I hope.

links:
(all are posts of mine - some may be more or less relevant but might help)
How I can read EF DbContext metadata programmatically?
How check by unit test that properties mark as computed in ORM model?
Get Model schema to programmatically create database using a provider that doesn't support CreateDatabase
Programmatic data transformation in EF5 Code First migration

3
5/23/2017 10:25:13 AM

Related Questions

Adding existing entities to a collection on a newly built object using the entity framework

"Attach" is not allowed because you haven't saved the order yet. Calling "Add" tells Entity Framework that you want to insert a new contact. So you are left with only one option. You need to load the contact....Here's the fastest way to do that:...OrderDetails context = new OrderDetails(); Contact contact = context.GetObjectByKey(new EntityKey("Ord...
entity-framework many-to-many
asked by Michael L Perry

AutoMapper + Entity Framework ( Entity to DTO and DTO to Entity )

The problem I had was related to updates to EntityCollection references. AutoMapper creates a new instance of the relation when mapping from the DTO to the Entity, and that doesn't please the EF....What solved my problem was configuring AutoMapper to use the destination value for my EntityCollection properties. In your case:...Mapper.CreateMap< Cus...
automapper c# dto entity-framework
asked by Pablo Montilla

LINQ to Entities only supports casting in the Entity Framework. basic kinds in the Entity Data Model

I know this is old, but I was looking to accomplish the exact same thing as the OP and didn't want to use the ...Func<IQueryable<T>, IOrderedQueryable<T>>... in my dictionary. Mostly because I would have to implement both an ...OrderBy... and ...OrderByDescending... delegate....I ended up creating an extension method for IQueryable called ...Object...
entity-framework primitive-types
asked by Lucifer Sam

Select * from Entities where Id = (select max(Id) from Entities) in Entity Framework

I think from a simplicity point of view, this should be same result but faster as does not require two round trips through EF to sql server, you always want to execute query as few times as possible for latency, as the Id field is primary key and indexed, should be performant...using(var db = new DataContext()) { var maxEntity = db.Entities.OrderBy...
entity-framework
asked by Gerard

In Entity Framework, several new entities might have the same primary key.

Assuming that the ...EmployeeID... in your database table is defined as ...INT IDENTITY..., then you could do this:...// create two new employees - one refers to the other Employee john = new Employee { EmployeeID = -1, EmpName = "John" }; Employee peter = new Employee { EmployeeID = -2, EmpName = "Peter", ReferEmployeeID = -1 }; // add them to th...
c# entity-framework
asked by marc_s

How to manually set entity primary key in Entity Framework code first database?

To allow you to manually generate Ids you need a class that has a manually generated ID - so it cannot inherit from ...DatabaseEntity...public class EbayCategory { [DatabaseGenerated(DatabaseGeneratedOption.None)] public int Id { get; set; } public string Name { get; set; } // ... some other properties } ...Now you will need ...
c# entity-framework primary-key
asked by Colin

Entity Framework - Updating entity with added/modified child and grandchild entities

Yes, you have to do that....When you do all the work inside a ...DbContext... scope it takes care to track al the changes happening in the entities, and you have to do nothing to let the DbContext know whathas changed....But, in multi-layered applications, when you move the entities between layers they cannot be kept inside a ...DbContext... scope,...
.net asp.net-web-api c# entity-framework entity-framework-6
asked by JotaBe

Dynamically querying two kinds of entities and mapping the results back to a specified entity collection

I hope this can help you...To search all cars by fueltype, use:...private static List<Car> SearchCars(List<Vehicle> vehicles, FuelType fueltype) { return vehicles.Where(f =>f is Car && (f as Car).FuelType == fueltype) .Select(x => (Car)x).ToList(); } ...If you want also filter by SerialNumber Use:...private static List<Car> SearchCar...
c# dapper entity-framework linq
asked by elfranchu

Entity Framework, Load multiple entities by primary key in a single query while still using caching

Not implicitly....Where()... will always query the database. To explicit query the cache you need to use ....Local...: ...dbContext.Entity.Local.Where(......This will not hit the database but it will only return entities that have been cached/loaded before....Good to know: to view the queries define a Log function like this: ...dbContext.Database.L...
.net c# entity-framework entity-framework-6
asked by Chris

Entity Framework Core "The entity type 'XXX' requires a primary key to be defined."

You can't define a composite key with data annotation alone. You need to use Fluent API instead. ...public class LectureCompletion { // which is your case. [ForeignKey(nameof(Lecture))] public int LectureId { get;set; } public Lecture Lecture { get; set; } [ForeignKey(nameof(ApplicationUser))] public int UserId {get;set;} ...
asp.net-core asp.net-identity c# entity-framework sql
asked by anserk

Fastest Entity Framework Extensions

Bulk Insert
Bulk Delete
Bulk Update
Bulk Merge
View more on Stack Overflow

Prime Library

Performance

Expression Evaluator

More Projects...

Related

Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow
Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow