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Better way to work with multiple databases

So the problem is: I am working with a legacy project. Creating a web interface to databases. ASP.NET Core, CRUD, that usual stuff. BUT!
There are 3(three) databases. Let's say there are Companies and Employees tables in each one of them. And there are Companies in the first database which employees may be found in first, second and third databases.
Currently, I am writing custom queries to target multiple databases. Working directly with MySqlConnection classes and MySqlDataReader.
It gets the job done, but I am really missing Entity Framework's lazy loading
I know I can create multiple EF contexts, one for each database, but it's not gonna work because as I said - data may be spread out through all 3 DB.
Is there any better way to communicate with multiple databases?

You can create synonyms in one database for tables located in another database and try to use it in EF.

Migrating data from 2 different SQL Server databases using console app

I have 2 web applications which are let's say Legacy1 and New1. I have separate DbContext for both applications and separate databases.
Now I want to migrate data from the Legacy1 database to the New1 database. I cannot simply use copy database or export database options in SQL Server. Entities are different and I need to incorporate some logic while migrating data.
I have decided to use .Net Core Console (.Net Framework) project to do this. Do I have to add both DbContexts to this project? Also all the entities which I want to map and do the migration or is there any other way to achieve this.

Finally i found a simple approach to achieve that. I used EF DB First approach to generate edmx files for source and target databases. Which gives me access to corresponding Entities as well.
I Queried source database using source dbcontext and manipulated data as per the requirements and inserted into target database using target dbcontext. I used AutoMapper to map source entities to Target entities.
It was much simpler than i thought earlier. Hope it helps others having similar scenario.

Having one DAL for 2 projects Entity Framework

I have 2 projects currently. A dashboard(MVC) and a API. both of them look at the same database but have their own models generated in their respective projects so if you make a change to one it doesn't reflect in the other one.
I want to add a third project for the data and have both my other projects look at that project for any data queries.
What would be the simplest way of doing this and how would the context of EF be affected with the queries sitting in a separate project from where the data is used.

Create a separate project for your Data Access Layer (EF en entities). Then create a reference to this separate project to use it.
Do not forget to add the connection string and entity framework setting to your .config file.
When do not work with code first and in your project you work with multiple Data layers, it may be required you add some metadata to the connection string.
I hope this helps u.

entity framework with two databases (completely different schemas )

I am very new to entity framework and I am trying to do something like following scenario.
I am creating ASP.net web from application. That website needs to connect to two databases which the schemas are completely different.
I have no idea how the basic structure should be.
I though of have EF on class library. please guide me with instructions since I have less knowledge.

Since you are using two different databases, the only viable option is to create two separate conceptual models. Even if you would be able to merge two different databases into a single conceptual model, it would be a pain to maintain is the databases are of mentionable sizes.
The two models could reside within the same project, in seprate folders to get different namespaces.
E.g.:
Company.MyApp.DataModel
Company.MyApp.DataModel.Model1
Company.MyApp.DataModel.Model2
Then you could put a new layer on top of these two models which do all the heavy lifting, and could even make them look like one database if you want that, or merge data from entities in both models into a DTO or something similar.
Check out the Repository pattern.

If you think about it, when you create a EDM model with Visual Studio it ask you to give an existing database, and when finished creating the model, it generates an EF connection string, that internally address to the given underlying database connection string.
E.g: metadata=res:///EFTestModel.csdl|res:///EFTestModel.ssdl|res:///EFTestModel.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.\;Initial Catalog=EFTest;Integrated Security=True;MultipleActiveResultSets=True"*
So each model matches only a database, only a connection string.
EF4 still does not support creating one conceptual model which works with N storage models. At least this is not supported with any built-in provider. Perhaps in the future this could be done through a new provider that combines the support of many storages (from the same providers or different).
I havent done enough research on it, but perhaps Windows Server AppFabric (Codename Velocity) could be the bridge to go through this gap.
Note: I have tried even editing manually the xml for the EDM (edmx) to insert a second element inside the tag but it does not match the EDM XML Schema so VS warns about it: Error 10021: Duplicated Schema element encountered.

You are going to use model first approach as the database already exists.
You will need to create two edmx for the two database.
You can create one model project which you can have connection strings for both the edmx in the app.config file and then create your edmx.

Possibility of multiple projects with Code First Entity Framework 5?

I would like to know if it's possible to create multiple projects with the same Entity framework 5(here Code First) and if you have a complete example?
I also want to use MVP pattern in my solution.
I've saw one problem: the database is created with the first run but just for one projects not all.
I know that's not really accurate... but I just want to know if it's possible..
Thanks in advance!

In my last project we developed a database which captures the business domain and we also stored security-related tables in the same database but in a different schema. The domain model in visual studio included all the tables, but data access was separated into two projects. The first one was a data access layer that deals with essential business tables, and another one was a custom security authentication which had mappings related to security tables.
In addition to this, to add to complexity :-), we also added a number of DbContext-inherited classes (in our DAL) that capture the essence of the domain with which a user is working. For example, Human Resources context deals with HR-related tables, Logistics context deals with logistical tables, etc.