EF Ccore 主从配置 最简化

业务需要 配置一主多从数据库 读写分离  orm用的ef core , 把思路和代码写下

1. 配置2个数据库上下文 ETMasterContext  ETSlaveContext(把增删改功能禁用掉)

public class ETMasterContext : DbContext
     {
         public ETMasterContext(DbContextOptions<ETMasterContext> options)
             : base(options)
         {

}

public DbSet<User> Users { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
             base.OnModelCreating(modelBuilder);

modelBuilder.ApplyConfiguration(new UserConfiguration());
         }
     }

public class ETSlaveContext : DbContext
     {
         public ETSlaveContext(DbContextOptions<ETSlaveContext> options)
             : base(options)
         {

}

public DbSet<User> Users { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
             base.OnModelCreating(modelBuilder);

modelBuilder.ApplyConfiguration(new UserConfiguration());

}
         public override int SaveChanges()
         {
             throw new InvalidOperationException("只读数据库,不允许写入");
         }
         public override int SaveChanges(bool acceptAllChangesOnSuccess)
         {
             throw new InvalidOperationException("只读数据库,不允许写入");
         }
         public override Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default)
         {
             throw new InvalidOperationException("只读数据库,不允许写入");
         }
         public override Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
         {
             throw new InvalidOperationException("只读数据库,不允许写入");
         }

}

2. 定义2个Repository  EfRepository(主)    EfReadOnlyRepository(只读)

public class EfRepository<T> : IRepository<T> where T : EntityBase
     {
         protected readonly ETMasterContext Context;

public EfRepository(ETMasterContext context)
         {
             Context = context;
             //Context.ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
         }

public IQueryable<T> Table => Context.Set<T>().AsQueryable();

public IQueryable<T> TableNoTracking => Context.Set<T>().AsNoTracking();

public int Delete(T entity)
         {
             try
             {
                 Context.Set<T>().Remove(entity);
                 return 1;
             }
             catch (Exception)
             {

return 0;
             }
         }

public int DeleteWhere(Expression<Func<T, bool>> criteria)
         {
             try
             {
                 IQueryable<T> entities = Context.Set<T>().Where(criteria);
                 foreach (var entity in entities)
                 {
                     Context.Entry(entity).State = EntityState.Deleted;
                 }
                 return 1;
             }
             catch (Exception)
             {
                 return 0;
             }

}

public T GetById(object id)
         {
             return Context.Set<T>().Find(id);
         }

public int Insert(T entity)
         {
             try
             {
                 Context.Set<T>().Add(entity);
                 return 1;
             }
             catch (Exception ex)
             {
                 return 0;
             }

}

public int InsertMany(IEnumerable<T> list)
         {
             try
             {
                 Context.Set<T>().AddRange(list);
                 return 1;
             }
             catch (Exception ex)
             {
                 return 0;
             }
         }

public int Update(T entity)
         {
             try
             {
                 Context.Entry(entity).State = EntityState.Modified;
                 return 1;
             }
             catch (Exception)
             {
                 return 0;
             }
         }
     }

public class EfReadOnlyRepository<T> : IReadOnlyRepository<T> where T : EntityBase
     {
         protected readonly ETSlaveContext Context;

public EfReadOnlyRepository(ETSlaveContext context)
         {
             Context = context;
             //Context.ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
         }

public IQueryable<T> Table => Context.Set<T>().AsQueryable();

public IQueryable<T> TableNoTracking => Context.Set<T>().AsNoTracking();

public T GetById(object id)
         {
             return Context.Set<T>().Find(id);
         }
     }

3. 用到的接口补上

public interface IReadOnlyRepository<T> where T : EntityBase

{
     IQueryable<T> Table { get; }

IQueryable<T> TableNoTracking { get; }
     T GetById(object id);

}

public interface IRepository<T> : IReadOnlyRepository<T> where T : EntityBase

{
     int Insert(T entity);
     int InsertMany(IEnumerable<T> list);
     int Update(T entity);
     int Delete(T entity);
     int DeleteWhere(Expression<Func<T, bool>> criteria);

}

4. Startup  ConfigureServices 中配置上下文

services.AddDbContext<ETMasterContext>(options =>
     options.UseMySql(GetConnectionStringByRandom("MySql_Master")));

services.AddDbContext<ETSlaveContext>(options =>
     options.UseMySql(GetConnectionStringByRandom("MySql_Slave")));

private string GetConnectionStringByRandom(string connectionString)

{
     var connstr = Configuration.GetConnectionString(connectionString);
     if (string.IsNullOrEmpty(connstr))
     {
         throw new Exception("数据库配置有误");
     }

var conList = connstr.Trim('|').Split('|');
     var rand = new Random().Next(0, conList.Length);
     return conList[rand];

}

5. appsetting.json 配置多个连接字符串  | 分隔

"connectionStrings": {
   "MySql_Master": "server=192.168.87.169;database=poker_games;uid=root;pwd=1$=6yuan;SslMode=None;",
   "MySql_Slave": "server=192.168.87.169;database=poker_games;uid=root;pwd=1$=6yuan;SslMode=None;|server=192.168.87.169;database=poker_games;uid=root;pwd=1$=6yuan;SslMode=None;"

}

6. 实际应用

public class ReportService : IReportService
     {
         private readonly IHttpContextAccessor _httpContextAccessor;
         private readonly IDistributedCache _distributedCache;
         private readonly IUnitOfWork _unitOfWork;
         private readonly IMapper _mapper;
         private readonly IReadOnlyRepository<Bet> _betRepository;

public ReportService(
             IHttpContextAccessor httpContextAccessor,
             IDistributedCache distributedCache,
             IUnitOfWork unitOfWork,
             IMapper mapper,
             IReadOnlyRepository<Bet> betRepository
             )
         {
             _httpContextAccessor = httpContextAccessor;
             _distributedCache = distributedCache;
             _unitOfWork = unitOfWork;
             _mapper = mapper;
             _betRepository = betRepository;
         }

}

public ReturnValue GetAgentBetReportByRound(AgentBetReportByRoundCriteriaModel reportModel)
         {

var betList = _betRepository.TableNoTracking.Where(p => p.pay_out_date >= beginTime && p.pay_out_date < endTime);
            
             return new ReturnValue(betList );

}

7. 大概解释下

如图 DBContext的生命周期默认是Scoped,即整个reqeust请求的生命周期以内共用了一个Context

利用这个生命周期 在每次请求时 通过配置文件获取不同的上下文实例 即实现了 多主多从 读写分离功能