I use the MDriven framework with custom OR mappings. The mapping mappens in a XML file which contains several classdefs and the database definition with the mapped tables.
As for now I have a 1:1 mapping between tables and classes. How does mapping of inheritance work in the mapping file?
My specific problem is a abstract base class which has "Children" mapping and two inherited classes that are mapped into a specific table each. A solution for this specific mapping case would help, but a general documentation of the mapping file and the different mapping types would be great.
Alternatively an answer to following question would also help: How can I generate a OR-mapping file for a default mapped model from the MDriven PersistanceMapper? The question above could then be reconstructed from the default OR mapping.
Easiest way to look at the ORMapping:
Start MDriven Designer - create a simple model - save it
Prototype by pressing play, choose SQL-persistence, pick a SQLExpress database, SQLCompact
Create database, Save script.
Look in the database for table ECO_ORMapping - here you have the ORMapping script
Alternative: Create a turnkey site - upload model, in cloud dialog choose "Admin db access and swap", Snapshot admin db, download admin db. You can open this db (sqlcompact) with linqpad
Related
I have been using Database First Entity Framework (EDMX) and SQL Server Data Tools Database Projects in combination very successfully - change the schema in the database and 'Update Model from Database' to get them into the EDMX. I see though that Entity Framework 7 will be dropping the EDMX format and I am looking for a new process that will allow me to use Code First in Combination with Database Projects.
Lots of my existing development and deployment processes rely on having a database project that contains the schema. This goes in source control is deployed along with the code and is used to update the production database complete with data migration using pre and post deployment scripts. I would be reluctant to drop it.
I would be keen to split one big EDMX into many smaller models as part of this work. This will mean multiple Code First models referencing the same database.
Assuming that I have an existing database and a database project to go with it - I am thinking that I would start by using the following wizard to create an initial set of entity and context classes - I would do this for each of the models.
Add | New Item... | Visual C# Items | Data | ADO.NET Entity Data Model | Code first from database
My problem is - where do I go from there? How do I handle schema changes? As long as I can get the database schema updated, I can use a schema compare operation to get the changes into the project.
These are the options that I am considering.
Make changes in the database and use the wizard from above to regenerate. I guess that I would need to keep any modifications to the entity and/or context classes in partial classes so that they do not get overwritten. Automating this with a list of tables etc to include would be handy. Powershell or T4 Templates maybe? SqlSharpener (suggested by Keith in comments) looks like it might help here. I would also look at disabling all but the checks for database existence and schema compatibility here, as suggested by Steve Green in the comments.
Make changes in code and use migrations to get these changes applied to the database. From what I understand, not having models map cleanly to database schemas (mine don't) might pose problems. I also see some complaints on the net that migrations do not cover all database object types - this was also my experience when I played around with Code First a while back - unique constraints I think were not covered. Has this improved in Entity Framework 7?
Make changes in the database and then use migrations as a kind of comparison between code and the database. See what the differences are and adjust the code to suit. Keep going until there are no differences.
Make changes manually in both code and the database. Obviously, this is not very appealing.
Which of these would be best? Is there anything that I would need to know before trying to implement it? Are there any other, better options?
So the path that we ended up taking was to create some T4 templates that generate both a DbContext and our entities. We provide the entity T4 a list of tables from which to generate entities and have a syntax to indicate that the entity based on one table should inherit from the entity based on another. Custom code goes in partial classes. So our solution looks most like my option 1 from above.
Also, we started out generating fluent configuration in OnModelCreating in the DbContext but have swapped to using attributes on the Entities (where attributes exist - HasPrecision was one that we had to use fluent configuration for). We found that it is more concise and easier to locate the configuration for a property when it is right there decorating that property.
I'm working with a legacy database that I can't easily create an entity model over because it uses extension tables with what is effectively composite keys and EF only supports single column keys for mapping one entity to multiple tables.
So, what I've decided to do is create updatable views (with INSTEAD OF triggers to handle CRUD operations) over the top of the legacy tables (which cannot be touched) and then have my entity model (either using EF or DevExpress XPO) built on top of the database views. This will also allow me to do stuff like easily add sub-queries in the select clause to retrieve child counts on parent records when retrieving a list of parent records in a single query.
However, I don't particularly want to manually write the SQL for all the views and triggers so I thought I'd use data model defined in the .EDMX file and t4 templates to help me generate the bulk of the T-SQL needed to create the views and the triggers. I thought there would be some template that I could use as the basis for doing this, but seems that's not so easy to find.
Can someone please suggest a t4 template that I could use as the basis where mappings are being retrieved from the .EDMX. Alternatively can anyone advise how to use the StorageMappingItemCollection to retrieve the mapping information from the EDMX file. I know a few people have said that apparently you can't use it or that they just use Linq to Xml, but I would have thought it should certainly be possible to use the StorageMappingItemCollection class as a strongly typed class to access this data.
Any examples of how I could use StorageMappingItemCollection to access mapping info would be very helpful. Thanks.
See http://brewdawg.github.io/Tiraggo.Edmx/ you can install it via NuGet within Visual Studio and it serves up all of the metadata from your EDMX files that Microsoft hides from you, very simple, works great.
Im currently working in a team that uses EF as the ORM of choice.
We have a common project that contains many EDMX files.
The reason for this is to keep the EDMX files small and manageable while also allowing them to focus on a conceptual set of tables on the database.
Eg
Orders.edmx
Users.edmx
Trades.edmx
These all point to a different set of tables on the same db.
I now need to add the user table to the Trade.edmx file. Since the user table is already in the user.edmx file, this creates the same User type twice under a different namespace which means I would need 2 UserRepository objects.
Common.data.trade.User
Common.data.users.User
Is there a way of avoiding 2 repository objects for the same table?
Any suggestions would be greatly appreciated
If you are using POCO generator you can update template for Trades.edmx to not generate new User class and its context template to use User class from Users namespace. EF matches POCO classes with entities in designer only by the class name (namespace is omitted) so it will work.
The disadvantage is that you have User entity in two mapping files and you must update it in both files or your application throw exception at runtime.
The reason for this problem is your architecture - at the beginning you wanted separated models but know you want to combine entities from different models. Those are contradicting requirements. Either use separated model where Trade knows only userID without any navigation property (like if it is defined in another database) or move all entities to single EDMX to support your new requirements.
I'm trying to kick off a project needing table-per-hierachy. I've done this in the past with NHibernate, but we want to avoid having to hand edit XML mapping files - so are trying to use Entity Framework and it's Designer.
I've been following this example online:
http://mosesofegypt.net/post/Inheritance-and-Associations-with-Entity-Framework-Part-1.aspx
When trying to select a Table from the "<Add Table or View>" dropdown, I can't select any tables, instead the list shows "(Empty)".
The only deviation I've made from the tutorial is that I didn't generate the Person table off the sample database, as far as I can tell this shouldn't make a difference (we want to generate the DB off the model, not vice versa).
Not sure what criteria a table needs to meet to be eligible to add a discriminator to...
If you need to generate DB from the model you cannot see any table in mapping because both mapping and information about tables is generated when you generate the database. EDMX has quite complex structure (much more complex than very easy hbm files for NHibernate). The complexity is even worse because EDMX doesn't have anything implicit - everything must be described and it must be described three times.
EDMX consists of three parts:
CSDL - conceptual model you see in the designer (classes)
SSDL - database description - this can be browsed in model browser but it is read-only
MSL - mapping between SSDL and MSL (that is what you are trying to edit in that window).
When you are going to use model-first (draw entities in designer and generate database) you define only CSDL and everything else is generated with SQL for the database. You will also probably need another template / workflow for DB generation because I guess it will by default use Table-per-type inheritance. Check Database generation power pack - it should contain template for TPH.
Trying to understand Entity Framework. My approach is database first. However I would like to define other entites in the model that is closer to my business objects. I guess I could write queries in the db and include them in the model. But I would also like to define entirely new entities in the model though they would be based on underlying tables in the db. How do I do that - does anyone know a tutorial?
Regards
Bjørn
db Oldtimer, EF Newbie
Database first means that you have existing database and you can either create model by updating from database or manually. You can use wizard to create initial model and modify it manually to define new entities but you must not use update from database any more or some of your changes will be deleted. Also your custom modifications must follow EF mapping rules (for example it is not directly possible to map multiple entities to the same table except some more advanced mapping scenarios like splitting and inheritance) and some of them (custom queries) must be done directly in EDMX source (XML) because designer doesn't support them - this requires more complex knowledge of EF mapping and it will be definitely hard for newbie.
You can check specification of that XML. For entities mapped to custom queries you will have to use DefiningQuery element in SSDL part of EDMX.