I did not see a resolution to this post so I thought I would ask this again using a tutorial as an example. I looked into this in EF4 and due to the limits I gave up. Now with EF6 I'm wondering if you can reference multiple databases or not.
For example, if you look at the Contonso University tutorial from Tom D you see a simple app using a single DB. What if all the people related data was contained in a separate DB. This would be the models like Person, Student, and Instructor which use the Person physical table. Can that be moved to a separate DB and have all the other functionality work without something like synonyms?
In a real world example we have separate databases for employee data and project data. We have an application for employee related information which can use just the employee DB with no problem. But you cannot build a project app without referencing the employee DB (to track who is working on what project). Ideally I want to build the employee app with EF and then turn around and leverage all that work with the project app. Then move on to a billing app which has another separate DB but would refer to both employee and project DBs.
I think the answer is "no" and this still can't be done but I want to get clarification.
Related
I have one project，need build more then 300 models, i want use EF codefirst.
But I think saved in one database Seems not so good.
so I want to know how to Save more then 300models to 5 database and use code first?
Do it right?
How to do it?
Have the mature example ?
how to query data by Navigate properties in tow models? They are not in same database，
I want query by lambda int these database like One database (on DbContext).
I am chinase .so English is very Bad.
I hope you can understand what I'm saying
The problem with splitting the models across multiple databases is that you cannot have foreign key relationships between the two databases.
If you are using multiple databases you will need to handle all the navigation yourself in code.
You should consider redesigning the database so that there are less base models and then using application level models to access the required models.
Another option is to use ubermodels keeping all 300 tables and then use application level models. This can be aided by techniques proposed in the article here on shrinking EF models that may help.
I'm working on a project (web application - ASP.NET MVC) that uses one database. Until now said database kept records for one client, but now I need to convert it to multi-client database. The idea is that we add a column (eg. CompanyId) to each Table in DB and in queries consider only records that have specific CompanyId.
Unfortunately, the project is quite developed right now and adding extra parameter to every service call, every Linq query etc would be really troublesome. I know that it should be approached this way (multi-client) from the beginning and now Im paying for it.
So I have two options:
Single database - the problem is how to tell EF to consider only records with CompanyId = X and not to write Where(i => i.CompanyId == X) in every single Linq query.
One DB = one client - creating one db for each client seems to be pretty good solution, but in our project user can have access to several databases (client can be associated with many companies and is asked to choose in context of which company he wants to work with and he can change it freely). The pronblem is I dont really know how to change connection string at runtime and I dont know if this solution is ok.
Could you please tell me which option is better and how to approach it?
Thank you in advance.
why don't you have separate but identical schemas for each company. You can then inject the right db context objects based on the company selected. In this way, you can avoid major db redactoring and also avoid the condition on company id.
I'm working on a project already started by several developers before me. One thing in particular bothers me is that they have single entity split in two databases.
Entity is called Tracker.
First database is called ConfigBase, and it has table named Trackers that has TrackerId along with it's attributes.
Second database is called StoreBase, and it also has table named Trackers, whose elements have matching TrackerId as it is in the first base.
Moreover, to have things even more complicated, when you access specific tracker in ConfigBase, you gain SQL server name and credentials that allow you to access it in StoreBase.
Now all this isn't too much complicated if you use plain old ADO.NET. But as my task is to raise entire solution to newest EF 4.3.1, I'm having troubles maintaining consistency of my entity. Half of things related to Tracker entity are in ConfigBase and the other half in StoreBase, and usually I have to get both to get some result.
Is there any solution to this that does not involve virtual merge on database level. I'm looking for a solution that can be done with Code First modelling.
Thanks in advance!
No there is no solution provided out of the box because EF itself is even not able to use more than one database per context. So you will either merge your databases or you will access each database separately (with separate Tracker entity per database) and merge data somehow in your application.
I've been playing about with the Entity 4 framework lately and it's pretty nifty. I've setup a class called Customer.cs with some properties like Name, Address etc. I also have a class called StoreEntities.cs which binds these back to the database through DbSet. It works fine and I can pull all my customers from the database.
The problem is every tutorial I come across on the internet generates their classes by hand. What I mean is, they all say something like "Now I'm going to make a new class called Orders with the following properties" and then proceed to write it out. That might be ok if I was starting a new project, but I'm porting over my old website so I have upwards of 20 tables in my database. If I go through and write all these out by hand I'm going to be there all week :D
Plus I'm not sure what would happen if I made some changes to the database (since I would have to go back through and update all my classes by hand).
I was hoping EF4 would have something similar to a Class Diagram, where I can point it at my database and have it generate a bunch of classes for me based on that.
I'm a little lost on this. Am I going about this the right way?
You should take a look at the ADO.NET C# POCO Entity Generator. With that you should be able to generate your model from your existing database and T4 templates will generate your POCO classes based on your databases tables, etc.
Here is a link to MSDN that explains how to Update Model from Database using the Update Model Wizard.
There are two ways to achieve what you want. Both start from adding new item to your project. In the "Add new item" window select "ADO.NET Entity Data Model". There you will have two options. One to generate your model from existing database and second to create model manualy in designer. If you choose first one you can simply drag and drop tables from server explorer to design surface and all your entities and their relations will be generated for you automaticaly. Also you can modify that generated model later.
I was wondering if EF4 support cross-databse relationships? For instance:
db1
Author
Id
Name
db2
Posts
Id
Content
db1.Author.Id
What ideally I need to do to get this relation in my ef4 model?
Do you guys have any idea?
Thanks
I've found this entry in Microsoft Connect that answers the question about the support given at this moment by EF (actually it is not supported yet).
Also found a thread in Social MSDN about this concern.
Other links on Stack Overflow:
ADO.Net Entity Framework across multiple databases
Entity framework 4 and multiple database
In summary, the only given alternatives are:
Using views in EF
Use NHibernate instead
If your database supports Synonyms, you can trick EF to span multiple databases. I wrote up how to do it here.
Basically you end up with an edmx file per database, and a script which merges them into a single edmx file. Synonyms are used to reference one database from another by using the actual table name, so EF doesn't throw a fit when you try to access database2.table from database1. You still have to setup links between the two databases manually in the EF model, but once setup they'll stay even if you re-run the merge script.
Scripts to setup Synonyms and to merge the edmx files are posted in the link
I recently began a project that uses entity framework with two databases, one Oracle and one SQL Server. I could not find any information regarding cross-database or multiple database support in the entity framework.
Most posts from the MS Entity framework team are a couple of years old and indicate that including two databases in a single model is not a feature that will be included soon. I would be interested in having a concrete answer on whether it was included in 2010 myself although I suspect the answer is no.
Currently out project gets around this limitation by having a separate entity model for each database. This has solved the problem for the majority of the scenarios we've encountered thus far in the project.
In cases where we've needed to query the data from the two databases at the same time, we simply created a view in one or the other databases. Since we're using Oracle and SQL Server, this view would utilize either a Linked Server (SQL) or a DBLink (Oracle).
The disadvantage of views in the entity framework is we've had to spent more time than I expected getting the primary keys working.
Hope this helps.