本文转自：https://docs.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

This article shows patterns for configuring a DbContext with DbContextOptions. Options are primarily used to select and configure the data store.+

Configuring DbContextOptions

DbContext must have an instance of DbContextOptions in order to execute. This can be configured by overriding OnConfiguring, or supplied externally via a constructor argument.+

If both are used, OnConfiguring is executed on the supplied options, meaning it is additive and can overwrite  options supplied to the constructor argument.+

Constructor argument

Context code with constructor+

public class BloggingContext : DbContext{    public BloggingContext(DbContextOptions<BloggingContext> options)        : base(options)    { }    public DbSet<Blog> Blogs { get; set; }}

Application code to initialize from constructor argument+

var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();optionsBuilder.UseSqlite("Filename=./blog.db");using (var context = new BloggingContext(optionsBuilder.Options)){    // do stuff}

OnConfiguring

Context code with OnConfiguring+

public class BloggingContext : DbContext{    public DbSet<Blog> Blogs { get; set; }    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)    {        optionsBuilder.UseSqlite("Filename=./blog.db");    }}

Application code to initialize with "OnConfiguring"+

using (var context = new BloggingContext()){    // do stuff}

Using DbContext with dependency injection

EF supports using DbContext with a dependency injection container. Your DbContext type can be added to the service container by using AddDbContext<TContext>.+

AddDbContext will add make both your DbContext type, TContext, and DbContextOptions<TContext> to the available for injection from the service container.+

See more reading below for information on dependency injection.+

Adding dbcontext to dependency injection+

public void ConfigureServices(IServiceCollection services){    services.AddDbContext<BloggingContext>(options => options.UseSqlite("Filename=./blog.db"));}

This requires adding a constructor argument to you DbContext type that accepts DbContextOptions.+

Context code+

public class BloggingContext : DbContext{    public BloggingContext(DbContextOptions<BloggingContext> options)      :base(options)    { }    public DbSet<Blog> Blogs { get; set; }}

Application code (in ASP.NET Core)+

public MyController(BloggingContext context)

Application code (using ServiceProvider directly, less common)+

using (var context = serviceProvider.GetService<BloggingContext>()){  // do stuff}var options = serviceProvider.GetService<DbContextOptions<BloggingContext>>();

+

Using IDbContextFactory<TContext>

As an alternative to the options above, you may also provide an implementation of IDbContextFactory<TContext>. EF command line tools and dependency injection can use this factory to create an instance of your DbContext. This may be required in order to enable specific design-time experiences such as migrations.+

Implement this interface to enable design-time services for context types that do not have a public default constructor. Design-time services will automatically discover implementations of this interface that are in the same assembly as the derived context.+

Example:+

using Microsoft.EntityFrameworkCore;using Microsoft.EntityFrameworkCore.Infrastructure;namespace MyProject{    public class BloggingContextFactory : IDbContextFactory<BloggingContext>    {        public BloggingContext Create()        {            var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();            optionsBuilder.UseSqlite("Filename=./blog.db");            return new BloggingContext(optionsBuilder.Options);        }    }}

More reading

• Read Getting Started on ASP.NET Core for more information on using EF with ASP.NET Core.

• Read Dependency Injection to learn more about using DI.

• Read Testing with InMemory for more information.

• Read Understanding EF Services for more details on how EF uses dependency injection internally.

[转] EF Configuring a DbContext