Can you tell Entity Framework to add an extra field for each field of a certain type? For example: Is it possible to generate a ChangedAt datetime field for each boolean field defined in the model, so this
public bool Confirmed { get; set; }
could result in a table with an additional field ConfirmedChangedAt where the value is updated each time the boolean value is changed.
Usually behavior like this should be implemented directly into your business logic and not automatically into the data layer. So I suggest to write something like this:
// entity
public class Order
{
public bool Confirmed { get; set; }
public DateTime? ConfirmedAt { get; set; }
}
// business logic
public class OrderManager
{
.................
public void Confirm( Order order )
{
// changing of entity status
order.Confirmed = true;
order.ConfirmedAt = DateTime.Now;
// storing new entity status
_orderRepository.Update( order );
................
}
}
I think if i understand you correctly, You are expecting the Entity Framework to be able to add columns to the database automatically so that you don't have to add them manually, Well you have 2 cases:
if you are using the database first approach you could achieve this
by using a query that's specific to your needs to add these columns
for you based on the conditions you have.
If you are using the code first approach and you have an existing database you may reverse engineer the database using the Entity Framework Power Tools and you could customize the T4 Templates to generate the entities with the extra properties that you need.
Plain answer no.
But it's depend on way how you interact with EF (code first, model first,database first).
If you using EF 6 and code first approach you can use idea of base Entity class
public class BaseEntity
{
public DateTime ChangedAt {get;set;}
}
public class ConcreteEntity : BaseEntity
{
public string Name {get;set;}
}
Now ConcreteEntity has ChangedAt by inheritance.
If this solution not for you, please explain question with more details.
The following class was Auto generated from a template using the Entity Framework Model.
namespace Entities
{
using System;
using System.Collections.Generic;
public partial class Country
{
public Country()
{
this.Regions = new HashSet<Region>();
}
public long CountryId { get; set; }
public string Code { get; set; }
public string Name { get; set; }
public bool Preferred { get; set; }
public System.DateTime LastChanged { get; set; }
public virtual ICollection<Region> Regions { get; set; }
}
}
I have a Wcf web service that returns POX (Xml) and Json only. I am wanting to return my own serialised object like;
public class MyResponseObject
{
public int RequestId {get;set;}
public List<Country> CountryList {get;set;}
//other properties
}
But I don't want to return the Regions ICollection.
The object can then be returned using something like
Newtonsoft.Json.JsonConvert.SerializeObject()
Am I best returning my own serialised POCO object in this manner ?
In projects like these, your classes can be split into two types:
Database entity objects (what Entity Framework works with)
Data contract objects (what WCF or your web-service works with)
While it is possible to use the same objects for both, it is not recommended because the database entity objects are an internal implementation concern that is separate from the external interface (your webservice). You might add or remove columns to your database table and not want your API contracts to change. But usually you'll want to hide information from service-consumers, like a database table Users ( UserId, Password ), you definitely don't want the Password property going out!
Another reason not to is that you later might want to add attributes to your webservice contract classes (e.g. to control output formatting or input validation), adding these to entity objects is painful, if not impossible in some cases.
I know it sounds like a needless duplication of work as the majority of classes will have identical members, but it makes sense from a long-term perspective.
Fortunately tools like AutoMapper can speed-up the process of copying data from your database entity objects to your data contract objects.
I'm having a problem with a mapping in Entity Framework.
I have the following classes (simplified):
public class Building
{
public int ID { get; set; }
// *.. snip..* other properties
public Location Location { get; private set; }
}
public class Location
{
public string Street {get; set;}
public Country country {get; set}
}
public class Country
{
public int ID { get; set; }
public string Name { get; set; }
}
Building and Country are entities, they are saved in the database. Location is a value type and should map to the same table as Building.
However, when I map it this way, entity framework wants to map Location to a table as well and is complaining it has no Key. I don't want to give it a key since it belongs to the Building and should not be an entity at all.
I have seen workarounds which say you need to put Country on the Building-class, but that just doesn't feel good (and is semantically just plain wrong).
I'm using Entity Framework 5
Since the release of Entity Framework Core 2, it is now possible to achieve this using owned entities.
Your configuration would look like:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// ...
modelBuilder.Entity<Building>().OwnsOne(x => x.Location);
modelBuilder.Entity<Location>().HasOne(x => x.Country);
// ...
}
This way, properties from Location class will be a part of the table Building class is mapped to. This means you will only have tables for Building and Country classes and the Building table will have a foreign key to the Country table.
I know it's been a long since you posted the question, but I thought this answer might be helpful to someone who comes across this question.
In my opinion the Entity Framework shouldn't allow such a case.
I understand that you don't consider the Location as an Entity but adding entity references to complex types doesn't seem like a solid approach either. The relationship of a building to a country is quite straight forward. A building belongs to one country. Thus a building model should include a country id. What would you expect to be mapped?
If you would expect the table Building to have just three columns ID, Street, CountryId and you still want to hold the Location model then you should use the following complex type.
public class Location
{
public string Street {get; set;}
public int countryId {get; set}
}
If however you would expect your Building table to have all the fields from the model Country then that could lead to some tricky situations like what would happen If you wanted to add new fields to the Country model or If you wanted to add other complex types or entities to your Country model according to a new Business Case.
Those cases would mess with the relational concept and would over-complicate your structure without any meaningful reason. (in my opinion of course)
You may mark Location property in Building class with [NotMapped] Attribute.
using System.ComponentModel.DataAnnotations.Schema;
public class Building
{
[NotMapped]
public Location Location { get; private set; }
}
Hope that solves your problem!
I'm having problems setting up an Entity Framework 4 model.
A Contact object is exposed in the database as an updateable view. Also due to the history of the database, this Contact view has two different keys, one from a legacy system. So some other tables reference a contact with a 'ContactID' while other older tables reference it with a 'LegacyContactID'.
Since this is a view, there are no foreign keys in the database, and I'm trying to manually add associations in the designer. But the fluent associations don't seem to provide a way of specifying which field is referenced.
How do I build this model?
public class vwContact
{
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class SomeObject
{
public virtual vwContact Contact { get; set; }
public int ContactId { get; set; } //references vwContact.KeyField
}
public class LegacyObject
{
public virtual vwContact Contact { get; set; }
public string ContactId { get; set; } //references vwContact.LegacyKeyField
}
ModelCreatingFunction(modelBuilder)
{
// can't set both of these, right?
modelBuilder.Entity<vwContact>().HasKey(x => x.KeyField);
modelBuilder.Entity<vwContact>().HasKey(x => x.LegacyKeyField);
modelBuilder.Entity<LegacyObject>().HasRequired(x => x.Contact).???
//is there some way to say which key field this reference is referencing?
}
EDIT 2: "New things have come to light, man" - His Dudeness
After a but more experimentation and news, I found using a base class and child classes with different keys will not work by itself. With code first especially, base entities must define a key if they are not explicitly mapped to tables.
I left the suggested code below because I still recommend using the base class for your C# manageability, but I below the code I have updated my answer and provided other workaround options.
Unfortunately, the truth revealed is that you cannot accomplish what you seek without altering SQL due to limitations on EF 4.1+ code first.
Base Contact Class
public abstract class BaseContact
{
// Include all properties here except for the keys
// public string Name { get; set; }
}
Entity Classes
Set this up via the fluent API if you like, but for easy illustration I've used the data annotations
public class Contact : BaseContact
{
[Key]
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class LegacyContact : BaseContact
{
public int KeyField { get; set; }
[Key]
public string LegacyKeyField { get; set; }
}
Using the Entities
Classes that reference or manipulate the contact objects should reference the base class much like an interface:
public class SomeCustomObject
{
public BaseContact Contact { get; set; }
}
If later you need to programmatically determine what type you are working with use typeof() and manipulate the entity accordingly.
var co = new SomeCustomObject(); // assume its loaded with data
if(co.Contact == typeof(LegacyContact)
// manipulate accordingly.
New Options & Workarounds
As I suggested in comment before, you won't be able to map them to a single view/table anyway so you have a couple options:
a. map your objects to their underlying tables and alter your "get/read" methods on repositories and service classes pull from the joined view -or-
b. create a second view and map each object to their appropriate view.
c. map one entity to its underlying table and one to the view.
Summary
Try (B) first, creating a separate view because it requires the least amount of change to both code and DB schema (you aren't fiddling with underlying tables, or affecting stored procedures). It also ensures your EF C# POCOs will function equivalently (one to a view and one to table may cause quirks). Miguel's answer below seems to be roughly the same suggestion so I would start here if it's possible.
Option (C) seems worst because your POCO entities may behave have unforseen quirks when mapped to different SQL pieces (tables vs. views) causing coding issues down the road.
Option (A), while it fits EF's intention best (entities mapped to tables), it means to get your joined view you must alter your C# services/repositories to work with the EF entities for Add, Update, Delete operations, but tell the Pull/Read-like methods to grab data from the joint views. This is probably your best choice, but involves more work than (B) and may also affect Schema in the long run. More complexity equals more risk.
Edit I'm not sure this is actually possible, and this is why:
The assumption is that a foreign key references a primary key. What you've got is two fields which are both acting as primary keys of vwContact, but depending on which object you ask it's a different field that's the primary key. You can only have one primary key at once, and although you can have a compound primary key you can't do primary key things with only half of it - you have to have a compound foreign key with which to reference it.
This is why Entity Framework doesn't have a way to specify the mapping column on the target side, because it has to use the primary key.
Now, you can layer some more objects on top of the EF entities to do some manual lookup and simulate the navigation properties, but I don't think you can actually get EF to do what you want because SQL itself won't do what you want - the rule is one primary key per table, and it's not negotiable.
From what you said about your database structure, it may be possible for you to write a migration script which can give the contact entities a consistent primary key and update everything else to refer to them with that single primary key rather than the two systems resulting from the legacy data, as you can of course do joins on any fields you like. I don't think you're going to get a seamlessly functional EF model without changing your database though.
Original Answer That Won't Work
So, vwContact contains a key KeyField which is referenced by many SomeObjects and another key LegacyKeyField which is referenced by many LegacyObjects.
I think this is how you have to approach this:
Give vwContact navigation properties for SomeObject and LegacyObject collections:
public virtual ICollection<SomeObject> SomeObjects { get; set; }
public virtual ICollection<LegacyObject> LegacyObjects { get; set; }
Give those navigation properties foreign keys to use:
modelBuilder.Entity<vwContact>()
.HasMany(c => c.SomeObjects)
.WithRequired(s => s.Contact)
.HasForeignKey(c => c.KeyField);
modelBuilder.Entity<vwContact>()
.HasMany(c => c.LegacyObjects)
.WithRequired(l => l.Contact)
.HasForeignKey(c => c.LegacyKeyField);
The trouble is I would guess you've already tried this and it didn't work, in which case I can't offer you much else as I've not done a huge amount of this kind of thing (our database is much closer to the kinds of thing EF expects so we've had to do relatively minimal mapping overrides, usually with many-to-many relationships).
As for your two calls to HasKey on vwContact, they can't both be the definitive key for the object, so it's either a compound key which features both of them, or pick one, or there's another field you haven't mentioned which is the real primary key. From here it's not really possible to say what the right option there is.
You should be able to do this with two different objects to represent the Contact view.
public class vwContact
{
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class vwLegacyContact
{
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class SomeObject
{
public virtual vwContact Contact { get; set; }
public int ContactId { get; set; } //references vwContact.KeyField
}
public class LegacyObject
{
public virtual vwLegacyContact Contact { get; set; }
public string ContactId { get; set; } //references vwLegacyContact.LegacyKeyField
}
ModelCreatingFunction(modelBuilder)
{
// can't set both of these, right?
modelBuilder.Entity<vwContact>().HasKey(x => x.KeyField);
modelBuilder.Entity<vwLegacyContact>().HasKey(x => x.LegacyKeyField);
// The rest of your configuration
}
I have tried everything that you can imagine, and found that most solutions won't work in this version of EF... maybe in future versions it supports referencing another entity by using an unique field, but this is not the case now. I also found two solutions that work, but they are more of a workaround than solutions.
I tried all of the following things, that didn't work:
Mapping two entities to the same table: this is not allowed in EF4.
Inheriting from a base that has no key definitions: all root classes must have keys, so that inherited classes share this common key... that is how inheritance works in EF4.
Inheriting from base class that defines all fields, including keys, and then use modelBuilder to tell wich base-properties are keys of the derived types: this doesn't work, because the methos HasKey, Property and others that take members as parameters, must reference members of the class itself... referencing properties of a base class is not allowed. This cannot be done: modelBuilder.HasKey<MyClass>(x => x.BaseKeyField)
The two things that I did that worked:
Without DB changes: Map to the table that is source of the view in question... that is, if vwContact is a view to Contacts table, then you can map a class to Contacts, and use it by setting the key to the KeyField, and another class mapping to the vwContacts view, with the key being LegacyKeyField. In the class Contacts, the LegacyKeyField must exist, and you will have to manage this manually, when using the Contacts class. Also, when using the class vwContacts you will have to manually manage the KeyField, unless it is an autoincrement field in the DB, in this case, you must remove the property from vwContacts class.
Changing DB: Create another view, just like the vwContacts, say vwContactsLegacy, and map it to a class in wich the key is the LegacyKeyField, and map vwContacts to the original view, using KeyField as the key. All limitations from the first case also applies: the vwContacts must have the LegacyKeyField, managed manually. And the vwContactsLegacy, must have the KetField if it is not autoincrement idenitity, otherwise it must not be defined.
There are some limitations:
As I said, these solutions are work-arounds... not real solutions, there are some serious implications, that may even make them undesirable:
EF does not know that you are mapping two classes to the same thing. So when you update one thing, the other one could be changed or not, it depends if the objects is cached or not. Also, you could have two objects at the same time, that represents the same thing on the backing storage, so say you load a vwContact and also a vwContactLegacy, changes both, and then try to save both... you will have to care about this yourself.
You will have to manage one of the keys manually. If you are using vwContacts class, the KeyFieldLegacy is there, and you must fill it. If you want to create a vwContacts, and associate is with a LegacyObject, then you need to create the reference manually, because LegacyObject takes a vwContactsLegacy, not a vwContacts... you will have to create the reference by setting the ContactId field.
I hope that this is more of a help than a disillusion, EF is a powerfull toy, but it is far from perfect... though I think it's going to get much better in the next versions.
I think this may be possible using extension methods, although not directly through EF as #Matthew Walton mentioned in his edit above.
However, with extension methods, you can specify what to do behind the scenes, and have a simple call to it.
public class LegacyObject
{
public virtual vwContact Contact { get; set; }
public string ContactId { get; set; } //references vwContact.LegacyKeyField
}
public class LegacyObjectExtensions
{
public static vwContact Contacts(this LegacyObject legacyObject)
{
var dbContext = new LegacyDbContext();
var contacts = from o in legacyObject
join c in dbContext.vwContact
on o.ContactId == c.LegacyKeyField
select c;
return contacts;
}
}
and
public class SomeObject
{
public virtual vwContact Contact { get; set; }
public int ContactId { get; set; } //references vwContact.KeyField
}
public class SomeObjectExtensions
{
public static vwContact Contacts(this SomeObject someObject)
{
var dbContext = new LegacyDbContext();
var contacts = from o in someObject
join c in dbContext.vwContact
on o.ContactId == c.KeyField
select c;
return contacts;
}
}
Then to use you can simply do like this:
var legacyContacts = legacyObject.Contacts();
var someContacts = someObject.Contacts();
Sometimes it makes more sense to map it from the other end of the relationship, in your case:
modelBuilder.Entity<LegacyObject>().HasRequired(x => x.Contact).WithMany().HasForeignKey(u => u.LegacyKeyField);
however this will require that u.LegacyKeyField is marked as a primary key.
And then I'll give my two cents:
if the Legacy db is using LegacyKeyField, then perhaps the legacy db will be read only. In this case we can create two separate contexts Legacy and Non-legacy and map them accordingly. This can potentially become a bit messy as you'd have to remember which object comes from which context. But then again, nothing stops you from adding the same EF code first object into 2 different contexts
Another solution is to use views with ContactId added for all other legacy tables and map them into one context. This will tax performance for the sake of having cleaner context objects, but this can be counteracted on sql side: indexed views, materialized views, stored procs, etc. So than LEGACY_OBJECT becomes VW_LEGACY OBJECT with CONTACT.ContactId brought over, then:
modelBuilder.Entity<LegacyObject>().ToTable("VW_LEGACY_OBJECT");
modelBuilder.Entity<LegacyObject>().HasRequired(x => x.Contact).WithMany().HasForeignKey(u => u.ContactId);
I personally would go with creating "mapper views" with CustomerId on legacy tables, as it's cleaner from c# layer perspective and you can make those views look like real tables. It is also difficult to suggest a solution without knowing what exactly is the scenario that you have a problem with: querying, loading, saving, etc.
In an application I'm working on, I have what are essentially a bunch of lookup tables in a database which all contain two things: The ID (int) and a Value (string).
There's only a handful of them, but I want to map all of them to a single Context which depends on the table name. Something like:
class LookupContext : DbContext
{
public DbSet<Lookup> Lookups { get; set; }
public LookupContext(String table)
{
// Pseudo code:
// Bind Lookups based on what table is
Lookups = MyDatabase.BindTo(table);
}
}
So if I create a new LookupContext("foo"), it binds against the foo table. If I do new LookupContext("bar") it uses the bar table, and so forth.
Is there any way to do this? Or do I have to create a separate context + model for every table I have?
This is more or less my first time doing this, so I'm not really sure if what I'm doing is right.
The answer we should be able to give you is to use enums, but that's not available quite yet - it's in the next version of EF. See here for details: http://blogs.msdn.com/b/adonet/archive/2011/06/30/walkthrough-enums-june-ctp.aspx
With earlier versions of EF, you can simply create a class per lookup value (assuming state as an example) and have code that looks something like the following:
public class State
{
public int StateId {get;set;}
public string StateName {get;set;}
}
public class LookupContext : DbContext
{
public DbSet<State> States {get;set;}
// ... more lookups as DbSets
}
This will allow you to use one context but will still require one class per table. You can also use the fluent API if you want your table/column names to differ from your class/property names respectively. Hope that helps!
I actually realized I was completely over complicating things beyond reason. There was no reason for storing multiple tables with two columns.
I'm better off storing my data as:
public class LookupValue
{
public string LookupValueId { get; set; }
public string Value { get; set; }
public string LookupType { get; set; }
}
Where the third field was simply the name of the table that I was previously storing in the database.
I'm still interested in the idea of mapping a single Context class to multiple tables, but I believe what I described above is the least convoluted way of accomplishing what I need.