使用实体框架核心的分片策略

Question

我正在使用Asp.Net Core和Entity Framework Core开发新的REST API。我们将移植来自使用水平数据库分区（分片）的旧版系统中的数据。我正在尝试一种在EF Core中处理此问题的好方法。我们以前的分片策略涉及一个中央Prime数据库和多个Customer数据库。所有查询都包含一个CustomerId。我们使用CustomerId查询Prime数据库，以确定哪个Customer数据库包含特定客户的数据。数据库模式如下所示：

主数据库

 dbo.Database  
        DatabaseId INTEGER  
        ConnectionString VARCHAR(200)  

    dbo.Customer  
        CustomerId BIGINT  
        DatabaseId INTEGER  

客户数据库

dbo.Order  
    CustomerId BIGINT  
    OrderId INT  
    ...  

用于获取订单的REST调用示例类似于 http://foo.com/api/Customers/{CustomerId}/Orders/{OrderId}

我需要在CustomerDbContext每个REST请求中使用动态确定的连接字符串。是否应DbContext为每个请求创建新的实例？或者，我可以在运行时更改连接字符串吗？

如果要创建新的DbContext，该如何处理？我可以找到的大多数示例代码都使用Startup.cs中的依赖注入来创建单例DbContext。

Answer 1

这是我想出的。它仍然很粗糙，我非常感谢您提出的任何批评。

我向dbo.Database添加了“ UseForNewCustomer BOOLEAN”。我正在使用数据库迁移来动态创建新的碎片。

ShardDbContextFactory

public class ShardDbContextFactory : IDbContextFactory<ShardDbContext>
{
    public ShardDbContext Create(DbContextFactoryOptions opts)
    {
        return this.Create("This-Connection-String-Isn't-Used");
    }

    public ShardDbContext Create(string connectionString)
    {
        var optsBldr = new DbContextOptionsBuilder<ShardDbContext>();
        //This is for PostGres. If using MS Sql Server, use 'UseSqlServer()'
        optsBldr.UseNpgsql(connectionString); 
        return new ShardDbContext(optsBldr.Options);
    }
}

ShardContextService.cs

public interface IShardContextService {
    ShardDbContext GetContextForCustomer(int customerId);
    void ActivateShard(string connectionString, string dbType);
}

public class ShardContextService : IShardContextService {
    private readonly PrimeDbContext _primeContext;
    public ShardContextService(SystemDbContext primeContext) {
        _primeContext = primeContext;
    }

    public CustomerDbContext GetContextForCustomer(int customerId)
    {
        Database shard = null;
        var customer = _primeContext.Customers
            .Include(m=>m.Database)
            .SingleOrDefault(c=>c.CustomerId == customerId);
        if (customer == null)
        {
            shard = _primeContext.Databases.Single(db=>db.UseForNewCustomer);

            if (shard == null) throw new System.Exception("Unable to determine shard: This is a new customer, and no shards are designated as useable for new customers.");

            _primeContext.Customers.Add(new Customer {
                CustomerId = customerId,
                DatabaseId = shard.DatabaseId
            });

            _primeContext.SaveChanges();
        }
        else
        {
            shard = customer.Database;
        }
        return (new ShardDbContextFactory()).Create(shard.ConnectionString)
    }

    public void ActivateShard(string connectionString)
    {
        using (var customerContext = (new ShardDbContextFactory()).Create(connectionString))
        {
            customerContext.Database.Migrate();
        }

        var previous = _primeContext.Databases.SingleOrDefault(d=>d.UseForNewCustomers);
        if (previous != null)
        {
            previous.UseForNewCustomers = false;
        }

        var existing = _primeContext.Databases.SingleOrDefault(d=>d.ConnectionString == connectionString);
        if (existing != null)
        {
            existing.UseForNewCustomers = true;
        }
        else
        {
            _primeContext.Databases.Add(new Database {
                ConnectionString = connectionString,
                UseForNewCustomers = true
            });
        }
        _primeContext.SaveChanges();
    }
}

用于创建新碎片的Controller Action

[HttpPost]
public IActionResult Shard([FromBody] string connectionString) {
    try {
        _shardContextService.ActivateShard(connectionString);
        return Ok("Shard activated");
    } catch (System.Exception e) {
        return StatusCode(500, e);
    }
}

用于查询的控制器操作

[HttpGet]
[Route("/api/Customers/{customerId}/Orders/{orderId}")]
public virtual IActionResult GetOrdersForCustomer([FromRoute]long customerId, [FromRoute] long orderId)
{
    using (var ctx = _shardContextService.GetContextForCustomer(customerId))
    {
        var order = ctx.Orders.Where(o => o.CustomerId == customerId && o.OrderId = orderId).Single();
        if (order == null) return NotFound("Unable to find this order.");
        else return new ObjectResult(order);
    }
}