mirror of https://github.com/abpframework/abp
Halil İbrahim Kalkan
6 years ago
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# Data Access
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# Connection Strings
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ABP framework was designed as database agnostic, it can work any type of data source by the help of the [repository](Repositories.md) and [unit of work](Unit-Of-Work.md) abstractions.
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ABP Framework is designed to be [modular](Module-Development-Basics.md), [microservice compatible](Microservice-Architecture.md) and [multi-tenancy](Multi-Tenancy.md) aware. Connection string management is also designed to support these scenarios;
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However, currently the following providers are implements:
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* Allows to set separate connection strings for every module, so every module can have its own physical database. Modules even might be configured to use different DBMSs.
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* Allows to set separate connection string and use a separate database per tenant (in a SaaS application).
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* [Entity Framework Core](Entity-Framework-Core.md) (works with [various DBMS and providers](https://docs.microsoft.com/en-us/ef/core/providers/?tabs=dotnet-core-cli).)
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* [MongoDB](MongoDB.md)
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* [Dapper](Dapper.md)
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It also supports hybrid scenarios;
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More providers might be added in the next releases.
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* Allows to group modules into databases (all modules into a single shared database, 2 modules to database A, 3 modules to database B, 1 module to database C and rest of the modules to database D... etc.)
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* Allows to group tenants into databases, just like the modules.
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* Allows to separate databases per tenant per module (which might be harder to maintain for you because of too many databases, but the ABP framework supports it).
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All the [pre-built application modules](Modules/Index.md) are designed to be compatible these scenarios.
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## Configure the Connection Strings
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See the following configuration:
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````json
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"ConnectionStrings": {
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"Default": "Server=localhost;Database=MyMainDb;Trusted_Connection=True;",
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"AbpIdentityServer": "Server=localhost;Database=MyIdsDb;Trusted_Connection=True;",
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"AbpPermissionManagement": "Server=localhost;Database=MyPermissionDb;Trusted_Connection=True;"
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}
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````
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> ABP uses the `IConfiguration` service to get the application configuration. While the simplest way to write configuration into the `appsettings.json` file, it is not limited to this file. You can use environment variables, user secrets, Azure Key Vault... etc. See the [configuration](Configuration.md) document for more.
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This configuration defines three different connection strings:
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* `MyMainDb` (the `Default` connection string) is the main connection string of the application. If you don't specify a connection string for a module, it fallbacks to the `Default` connection string. The [application startup template](Startup-Templates/Application.md) is configured to use a single connection string, so all the modules uses a single shared database.
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* `MyIdsDb` is used by the [IdentityServer](Modules/IdentityServer.md) module.
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* `MyPermissionDb` is used by the [Permission Management](Modules/Permission-Management.md) module.
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[Pre-built application modules](Modules/Index.md) define constants for the connection string names. For example, the IdentityServer module defines a ` ConnectionStringName ` constant in the ` AbpIdentityServerDbProperties ` class (located in the ` Volo.Abp.IdentityServer ` namespace). Other modules similarly define constants, so you can investigate the connection string name.
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## Set the Connection String Name
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A module typically has a unique connection string name associated to its `DbContext` class using the `ConnectionStringName` attribute. Example:
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````csharp
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[ConnectionStringName("AbpIdentityServer")]
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public class IdentityServerDbContext
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: AbpDbContext<IdentityServerDbContext>, IIdentityServerDbContext
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{
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}
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````
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For [Entity Framework Core](Entity-Framework-Core.md) and [MongoDB](MongoDB.md), write this to your `DbContext` class (and the interface if it has).
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> If you are developing a reusable, database provider independent module see also [the best practices guide](Best-Practices/Index.md).
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## Database Migrations for the Entity Framework Core
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Relational databases require to create the database and the database schema (tables, views... etc.) before using it.
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The startup template (with EF Core ORM) comes with a single database and a `.EntityFrameworkCore.DbMigrations` project that contains the migration files for that database. This project mainly defines a *YourProjectName*MigrationsDbContext that calls the `Configure...()` methods of the used modules, like `builder.ConfigurePermissionManagement()`.
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Once you want to separate a module's database, you typically will need to create a second migration path. The easiest way to create a copy of the `.EntityFrameworkCore.DbMigrations` project with the `DbContext` inside it, change its content to only call the `Configure...()` methods of the modules needs to be stored in the second database and re-create the initial migration. In this case, you also need to change the `.DbMigrator` application to be able to work with these second database too. In this way, you will have a separate migrations DbContext per database.
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## Multi-Tenancy
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See [the multi-tenancy document](Multi-Tenancy.md) to learn how to use separate databases for tenants.
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