实体框架和多个模式 [英] Entity Framework and multiple schemas

问题描述

我试图建立我的DbContext，以便它可以处理单个Oracle数据库多种模式。我不想一个整体的DbContext文件，所以我想出了以下内容：

I'm trying to set up my dbContext so that it can handle multiple schemas in a single Oracle database. I didn't want one monolithic dbContext file so I've come up with the following:

public class oraDbContext : DbContext
{
    static oraDbContext() {
        Database.SetInitializer<oraDbContext>(null);
    }

    public oraDbContext(string connName)
        : base("Name=" + connName) { }

    public _schema1 schema1 = _schema1.Instance;
    public _schema2 schema2 = _schema2.Instance;

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        schema1.OnModelCreating(modelBuilder);
        schema2.OnModelCreating(modelBuilder);
    }
}

模式文件看起来是这样的：

The schema file looks like this:

public sealed class _schema1
{
    private static readonly _schema1 instance = new _schema1();

    static _schema1() { }
    private _schema1() { }

    public static _schema1 Instance {
        get {
            return instance;
        }
    }

    public DbSet<someTable> someTable { get; set; }

    internal void OnModelCreating(DbModelBuilder modelBuilder) {
        modelBuilder.Configurations.Add(new someTableMap());
    }
}

然而，当我试图执行一个查询我得到的错误：值不能为空。它所指的值是_schema1在 someTable 属性。

However, when I try to perform a query I get the error: Value cannot be null. The value it's referring to is the someTable property in _schema1.

一个。我该如何解决这个问题？

A. How can I fix this?

乙。有没有更好的解决办法？

B. Is there a better solution?

编辑：我想在这里写code的能力，比如下面 -

What I want here is the ability to write code such as the following -

var query1 = from p in db.schema1.someTable
             select p;
var query2 = from p in db.schema2.someTable
             select p;

在哪里someTable是两种模式是相同的。在我们的数据库中，我们有几个模式与具有相同或几乎相同的列完全相同的表。我不想为每个模式一个单独的DbContext，因为这可能意味着5种不同的连接，如果我创建，从5模式拉查询。如果我在写SQL直同一查询，我可以拉5种不同模式的数据与单个连接，这就是我想在这里完成的。

Where someTable is the same in both schemas. In our database we have several schemas with the exact same tables that have identical or nearly identical columns. I don't want to create a seperate dbContext for each schema because that could potentially mean 5 different connections if I'm creating a query that pulls from 5 schemas. If I was writing this same query in straight SQL I could pull the data from 5 different schemas with a single connection and that's what I would like to accomplish here.

推荐答案

虽然做一些研究关于实体框架我碰上了以下职位：

While doing some research about Entity Framework I came across the following post:

HTTP： //romiller.com/2011/05/23/ef-4-1-multi-tenant-with-$c$c-first/

这并不完全给我一个单一的DbContext一起工作，但它只能使用一个连接（这是我的身后不想使用多个dbContexts推理）。设置以下code之后：

It doesn't quite give me a single dbContext to work with but it does only use a single connection (which was my reasoning behind not wanting to use multiple dbContexts). After setting up the following code:

public class oraDbContext : DbContext
{
    static oraDbContext() {
        Database.SetInitializer<oraDbContext>(null);
    }

    private oraDbContext(DbConnection connection, DbCompiledModel model)
        : base(connection, model, contextOwnsConnection: false) { }

    public DbSet<SomeTable1> SomeTable1 { get; set; }
    public DbSet<SomeTable2> SomeTable2 { get; set; }

    private static ConcurrentDictionary<Tuple<string, string>, DbCompiledModel> modelCache = new ConcurrentDictionary<Tuple<string, string>, DbCompiledModel>();

    public static oraDbContext Create(string schemaName, DbConnection connection) {
        var compiledModel = modelCache.GetOrAdd(
            Tuple.Create(connection.ConnectionString, schemaName),
            t =>
            {
                var builder = new DbModelBuilder();
                builder.Configurations.Add<SomeTable1>(new SomeTable1Map(schemaName));
                builder.Configurations.Add<SomeTable2>(new SomeTable2Map(schemaName));

                var model = builder.Build(connection);
                return model.Compile();
            });

        return new oraDbContext(connection, compiledModel);
    }
}

这当然需要，我的映射文件设置像这样：

This of course requires that my mapping files be set up like so:

public class DailyDependencyTableMap : EntityTypeConfiguration<DailyDependencyTable>
{
    public SomeTableMap(string schemaName) {
        this.ToTable("SOME_TABLE_1", schemaName.ToUpper());

        //Map other properties and stuff
    }
}

这是使用多种模式编写查询是有点恼人，但就目前而言，它做什么，我需要做的：

Writing queries that use multiple schemas is somewhat annoying but, for the moment, it does what I need it to do:

using (var connection = new OracleConnection("a connection string")) {
    using (var schema1 = oraDbContext.Create("SCHEMA1", connection))
    using (var schema2 = oraDbContext.Create("SCHEMA2", connection)) {

        var query = ((from a in schema1.SomeTable1 select new { a.Field1 }).ToList())
             .Concat((from b in schema2.SomeTable1 select new { b.Field1 }).ToList())
    }
}

＆NBSP;

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