Comments (44)
  1. Chris Hohmann says:

    I think this is certainly a step in the right direction, but what i would really like to see is mutable entity keys. Without this, Entity Framework is not suitable for any database that happens to use natural keys instead of surrogate keys. One glaring example of this is the Customers table in Microsoft's Northwind database.

  2. Remco Blok says:

    Although this article has screenshots of entities in the designer and examples of the xml metadata, can I assume the DbContext / Code First approach will also be supported?

  3. dpblogs says:

    Yes, we would support this in DbContext and Code First

  4. drasto says:

    The most important feature would of cause be that when entity specified using property that has unique constraint on and that entity will be found in context database will not be hit.

  5. rjfhendriks says:

    Hi, good the see some progress in this area. You are taking it far!

    Wat I really would like to see supported is the possibility to define an unique key on an N:M table with a PK ID and a UK on the 2 foreign keys to the PK's of the N and M table with other properties. We now parse the unique key database error according to it's type (Oracle / sql server) .. 🙂

  6. Bob Kolo says:

    I would love to see associations on unique constraints. We use these a fair amount in our production database where certain primary keys need to be kept private.

  7. Ben Vitale says:

    We absolutely need associations on unique constraints. That is quite prevalent in our legacy schema. The property on the principal end needs to be mutable to null and support cascade delete.


  8. MolallaComm says:

    For code first, would you add a [Unique] meta data annotation or something similar?  Also, I agree with Ben on the mutable to null part, which makes the t-sql generated for the constraint a little less portable in that I believe only SQL2008 and later support filtered indexes which allow you to have more than one NULL row at a time (i.e. CREATE UNIQUE NONCLUSTERED INDEX [IX_GponOntPort_CircuitID_Unique] ON [dbo].[GponOntPort](CircuitID) WHERE CircuitID IS NOT NULL).

  9. Ken Smith says:

    You asked: "Do you see the need to form associations using unique constraints where you are associating to a unique constraint on the principal end instead of the primary key on that entity? Is this something you see in existing/legacy databases?"

    And the answer on my end, at least, is: Yes, this is very much something we would like to use in our databases, and can't now, because of this particular EF limitation.  Specifically, imagine a database that uses surrogate keys for all tables, and has the following hierarchy: User->Contact->ContactGroup<-Group<-User.  In other words, both the Group and the Contact tables belong to the User, and hence, it makes sense to allow a ContactGroup to join a Contact and a Group if they both belong to the same user.  The best way I've found to do model this is to add the UserId table to ContactGroup, add a unique key to Contact and to Group which includes the UserId, and add foreign keys from ContactGroup to Contact and Group which are based on their unique keys rather than their primary keys.

    That said, perhaps there's a better way to model this….?

  10. Simon Francesco says:

    +1 to associations to unique constraints. Also yes to mutability of these constraints. For example we have several FKs in our databases that link attributes of a transaction to the transaction line based on a composite unique key. We would hope to be able to change the transaction line, have the change cascade to the attribute rather than have to delete the attribute, change the transaction line and then create the new attribute.

    While these are underlying features, it is important to follow up new features with designer support and code generation. It is *painful* maintaining metadata by hand that is available from the database when it could be automatically handled eg defaults, validation, identity attributes, … they all need pushing through the SSDL and CSDL.

  11. Youhei Kondou says:

    There is a missing point for UNIQUE CONSTRAINT. The name is "unique constraint for multiple columns". It's important for environment in "Single primary key" convention. I use "unique constraint for multiple columns" instead of "primary keys for multiple columns".

  12. Preetham says:

    When is this feature going to be available? I want to build bi-directional one-one relationships and it can't happen without have unique constraints…

  13. Aaron says:

    Yes, we definitely have a need for candidate key relationships. This would be a huge addition for us in adopting Entity Framework as our core framework for data access.

  14. Surrogate or not, mutable primary keys are a bad idea.

  15. Associations based on unique constraints is definately a good idea but I can live without it. More important is having the ability to define a unique constraint.

  16. Matt says:

    +1 to associations to unique constraints. It's overly simplistic to expect an entity to have only one unique key to create associations on. Any potential timescales on this feature?

  17. David Sherwood says:

    I would hope with unique constraint support you would provide routines to check if a change or add would violate the constraint. Possible just another form of the DbSet find routine. It is necessary to check this before saving changes and I assume that since you are enforcing the unique constraint any way that you would have more efficient routines that just a general Linq query.

  18. Pete Mack says:

    I am confused about what release this will be in. (I am trying it in EF 4.2 with no luck.)

    This would be a huge win for us, since we often want our primary key to include a Date column in the clustered key for data (not metadata) tables for performance, but we wish to use only the Identity column for referential constraints.

    We are faking it now, by:

    * Leaving the Date field out of the primary key.

    * Updating the generated ddl so that the PK is NONCLUSTERED

    * Adding a Unique clustered constraint on (Date, Identity)

    Unfortunately, there's a nasty post-build step to update the PK declaration, as NONCLUSTERED is also not an EF attribute on indexes.

  19. Pete Mack says:

    Another comment on member attributes.

    We have another problem, in that would like to include user-friendly XML serialization in the same data model.

    We are doing it now with Code-First programming, but this falls down quickly for complex data models.

    We have a potential work-around: overload the "Long Description" to encode the additional attributes, and add any additional xml serialization fields to an external partial class declaration.

    This requires a new .tt file that parses Long Description, and it isn't at all pretty.

  20. Jonny says:

    I cannot believe you haven't already got Unique Constraint support.  You said "We’ve been busy working on enabling unique constraints in the Entity Framework", more like "oh sh*t, we forgot to add this important feature, we best get that fixed and rolled out ASAP!".  True to form, the Worlds biggest, but always one step behind the rest!  No wonder people are leaving the Microsoft fold for pastures new!  

  21. soham says:

    please support the creating of unique constraints already!

    any timelines when we could expect this feature?

  22. Joe says:

    I too am anxious for unique constraints. When?

  23. Jon says:

    I have an immediate need for "Associations based on unique constraints." I am working with a legacy database that was designed poorly and as a result I need it badly. Personally, I would be fine with only supporting linking to a primary key, but, since there are a lot of existing screwed up databases out there, it would be very helpful.

  24. Doug Clutter says:

    I just read a post on StackOverflow that said EF v5.0 will NOT support unique constraints.  That's really a shame.  As you illustrate so well in this posting, it is an extremely useful part of any ORM toolkit.  Please consider adding it to v5.0 before you ship.  Thanks.

  25. Sounds awesome.  Unique constraint support is greatly needed.  Please prioritize.

  26. Mert says:

    Unique constraint should be easily configured using Fluent API.

  27. Justin says:

    Suppose you've got a table that describes an ordered list of things. The table might have columns for ThingId, ThingTitle, and ThingPositionIndex, where ThingPositionIndex must be unique. Even if the Entity Framework supported unique constraints somehow, I doubt they'd be enforced properly; I don't think SQL Server can do it. If you attempted to swap the order of two things the submit would fail because the unique constraint index is checked after each row update. What you really need is some type of constraint checking that happens at the end of a transaction or some form of a multi-update/delete/insert.

  28. Jerome Haltom says:

    Any update on this? Every year or so for the last 4 years I've tried to migrate my database from NHibernate to EF… and despite there being an entirely new version each time, this is a stopper. =/

  29. Gabriel Vonlanten C. Lopes says:

    This is a must! I have stumped with this issue every now and then. Please consider adding this!

  30. Renato Lima says:

    Stuck at the same problem, I have a product in final development phase, and at this point we have no alternative solution. Is it planned to be implemented on EF6?

  31. Karl says:

    same problem, this is a very urgent issue in my development,, any chance to get in EF6?

  32. David says:

    Well this is one EF fanboy who just shot himself in the foot. Seriously MS? Get your act together!

  33. I am very disappointed to learn the EF5 doesn't support Unique constraints! This is such a heavily requested feature and so easily implemented! Why hasn't it been done yet!?!? If EntityFramework is to compete with behemoths like NHibernate, you MUST stay stay relevant and responsive to requests of your users… over 2 years to release an important feature like this is not acceptable…

  34. John Carroll says:

    Every release of entity framework seems to contain features that are of little, if any use, in real word scenarios.

    Something like unique constraints which a large portion of the use community wants is clearly not exotic enough for the developers

  35. Hans says:

    I use modeling tools now for 30 years. vs2012 is the first tool I ever found, that cannot model a unique constraint.  The tools of IBM and Oracle can do it.

  36. nick d says:

    Come on guys – it's 2013, where is this? [Unique] constraint data annotation is badly needed and very basic requirement.

  37. Chris says:

    Is this going to happen? EF 6 is just about released and this is a pretty big feature to leave out.

  38. Steve says:

    Can't see any evidence in the EF 6 documentation about this feature :(. Would be good to get some confirmation from MS about when we can expect this feature to appear.

  39. batpox says:

    It didn't make the cut again? Unbelievable!

  40. lucaster says:

    Still no unique constraint? YOU MUST BE F*INKTROLLING

  41. Tim says:

    Whhaaaaat! Surely this is a joke… Half a job yet again, thanks a bunch Microsoft.

  42. Thanmal says:

    Why can't someone from MS at least comment as to what is going on with this feature? Is it just ineptitude or complete ignorance? Please suggest is this feature request is dead or is there any timeline on this?

    This is such a basic and required feature where you need to associate by unique keys and not by primary keys?

  43. AxelD says:

    Here's my suggestion for implementing a UniqueKey annotation in Code First:…/572705

    In this thread I'm suggesting an annotation syntax for table indices, but the semantics should be the same for unique keys, as they may span several columns of a table.

    In addition to table unique keys, there should be a column UniqueKey data annotation, too, to simplify single column unique keys.

    In addition, foreign keys referencing unique keys could simply be set using the ForeignKey data annotation, added to then navigation property.

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