asp.net-core-mvc – 创建多个dbcontexts的MVC 6 EF7 RC1

public class DecAppContext : DbContext
    {

        public DecAppContext()
          //  :base("DefaultConnection")
        {

        }
        public DbSet<VignetteModels> VignetteModels { get; set; }
        public DbSet<VignetteResult> Result { get; set; }
    }
}

"Data": {
    "DefaultConnection": {
      "ConnectionString": "Server=(localdb)mssqllocaldb;Database=aspnet5-xxxxx...;Trusted_Connection=True;MultipleActiveResultSets=true"
    }
  }

services.AddEntityFramework()
                .AddSqlServer()
                .AddDbContext<ApplicationDbContext>(options =>
                    options.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]))
                .AddDbContext<DecAppContext>(options => options.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));

private DecAppContext db = new DecAppContext();
var vignette = db.VignetteModels.SingleOrDefault(v => v.CaseId == vid);

首先,我会从GitHub上的EntityFramework的wiki推荐你 the article.本文介绍了许多定义DbContext的方法,它引用了appsettings.json的一部分.我个人更喜欢使用[FromServices]属性的方式.

代码可以是以下内容：

首先,您使用以下内容定义了appsettings.json

{
  "Data": {
    "ApplicationDbConnectionString": "Server=(localdb)mssqllocaldb;Database=ApplicationDb;Trusted_Connection=True;MultipleActiveResultSets=true","DecAppDbConnectionString": "Server=Server=(localdb)mssqllocaldb;Database=DecAppDb;Trusted_Connection=True;MultipleActiveResultSets=true"
  }
}

您在其中定义两个连接字符串.

几秒钟,你声明了以DbContext为基类的类DecAppContext和ApplicationDbContext.最简单的形式就是

public class ApplicationDbContext : DbContext
{
}
public class DecAppContext : DbContext
{
}

没有任何DbSet属性.

第三步.您使用Microsoft.Extensions.DependencyInjection注入数据库上下文.要做到这一点,你需要在Startup.cs中加入类似的内容

public class Startup
{
    // property for holding configuration
    public IConfigurationRoot Configuration { get; set; }

    public Startup(IHostingEnvironment env)
    {
        // Set up configuration sources.
        var builder = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddEnvironmentVariables();
        // save the configuration in Configuration property
        Configuration = builder.Build();
    }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        // Add framework services.
        services.AddMvc()
            .AddJsonOptions(options => {
                options.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
            });
        services.AddEntityFramework()
            .AddSqlServer()
            .AddDbContext<ApplicationDbContext>(options => {
                options.UseSqlServer(Configuration["Data:ApplicationDbConnectionString"]);
            })
            .AddDbContext<DecAppContext>(options => {
                options.UseSqlServer(Configuration["Data:DecAppDbConnectionString"]);
            });
    }
    public void Configure(IApplicationBuilder app,IHostingEnvironment env,ILoggerFactory loggerFactory)
    {
        ...
    }
}

使用配置“Data：DecAppDbConnectionString”和“Data：ApplicationDbConnectionString”创建两个DbContext(DecAppContext和ApplicationDbContext).

现在我们可以在控制器中使用上下文.例如

[Route("api/[controller]")]
public class UsersController : Controller
{
    [FromServices]
    public ApplicationDbContext ApplicationDbContext { get; set; }

    [FromServices]
    public DecAppContext DecAppContext { get; set; }

    [HttpGet]
    public IEnumerable<object> Get() {
        var returnObject = new List<dynamic>();

        using (var cmd = ApplicationDbContext.Database.GetDbConnection().CreateCommand()) {
            cmd.CommandText = "SELECT Id,FirstName FROM dbo.Users";
            if (cmd.Connection.State != ConnectionState.Open)
                cmd.Connection.Open();

            var retObject = new List<dynamic>();
            using (var dataReader = cmd.ExecuteReader())
            {
                while (dataReader.Read())
                {
                    var dataRow = new ExpandoObject() as IDictionary<string,object>;
                    for (var iFiled = 0; iFiled < dataReader.FieldCount; iFiled++)
                        dataRow.Add(
                            dataReader.GetName(iFiled),dataReader.IsDBNull(iFiled) ? null : dataReader[iFiled] // use null instead of {}
                        );

                    retObject.Add((ExpandoObject)dataRow);
                }
            }
            return retObject;
        }
    }
}

或使用async / await相同：

[Route("api/[controller]")]
public class UsersController : Controller
{
    [FromServices]
    public ApplicationDbContext ApplicationDbContext { get; set; }

    [FromServices]
    public DecAppContext DecAppContext { get; set; }

    [HttpGet]
    public async IEnumerable<object> Get() {
        var returnObject = new List<dynamic>();

        using (var cmd = ApplicationDbContext.Database.GetDbConnection().CreateCommand()) {
            cmd.CommandText = "SELECT Id,FirstName FROM dbo.Users";
            if (cmd.Connection.State != ConnectionState.Open)
                cmd.Connection.Open();

            var retObject = new List<dynamic>();
            using (var dataReader = await cmd.ExecuteReaderAsync())
            {
                while (await dataReader.ReadAsync())
                {
                    var dataRow = new ExpandoObject() as IDictionary<string,object>;
                    for (var iFiled = 0; iFiled < dataReader.FieldCount; iFiled++)
                        dataRow.Add(dataReader.GetName(iFiled),dataReader[iFiled]);

                    retObject.Add((ExpandoObject)dataRow);
                }
            }
            return retObject;
        }
    }
}

可以只声明属性public ApplicationDbContext ApplicationDbContext {get;组;使用属性[FromServices]和ASP.NET从ConfigureServices中注入的上下文初始化它.以同样的方式,您可以在需要时使用第二个上下文DecAppContext.

上面的代码示例将在数据库上下文中执行SELECT Id,FirstName来自dbo.Users并返回格式为[{“id”：123,“firstName”：“Oleg”},{“id”：456,“名字 “：” Xaxum“}].由于在ConfigureServices中使用AddJsonOptions,因此在序列化期间将自动将Id和FirstName的属性名称转换为id和firstName.

更新：我必须参考the announcement.下一版本的MVC(RC2)将需要更改上面的代码以使用[FromServices]作为附加参数(例如方法Get())而不是使用公共属性[FromServices] public ApplicationDbContext ApplicationDbContext {get;组; }.需要删除属性ApplicationDbContext并向Get()方法添加其他参数：public async IEnumerable< object>获取([FromServices] ApplicationDbContext applicationDbContext){…}.这样的改变很容易完成.请参阅here以及MVC演示示例中的更改示例：

[Route("api/[controller]")]
public class UsersController : Controller
{
    [HttpGet]
    public async IEnumerable<object> Get(
                     [FromServices] ApplicationDbContext applicationDbContext,[FromServices] DecAppContext decAppContext)
    {
        var returnObject = new List<dynamic>();

        // ...  the same code as before,but using applicationDbContext 
        // and decAppContext parameters instead of ApplicationDbContext
        // and DecAppContext properties
    }