作者 | 喵叔

责编 | 刘静

出品 | CSDN（ID：CSDNnews）

public class EFContext : DbContext
{protected override void OnModelCreating(ModelBuilder modelBuilder){modelBuilder.Entity<Employee>().HasQueryFilter(p => !p.IsDelete);modelBuilder.Entity<Department>().HasQueryFilter(p => !p.IsDelete);base.OnModelCreating(modelBuilder);}
}

上面这段代码大部分人看完一定觉得没有问题，但是我要告诉各位的是这段代码有一个很大的问题，就是每次去操作 Employee 或 Department 实体时都会应用 HasQueryFilter , 那么如果由几十个甚至上百个 Model 的时候，如果按照上述的方式来编写代码的话那么我们将会配置 HasQueryFilter 几十次上百次。那么问题来了，着这种情况下我们应该怎样支持多租户，应该怎样实现软删除，以及应该怎样实现模型查询过滤的自动检测。下面我们就来一个问题一个问题的讲解。

准备基础代码

/// <summary>
/// 实体基类
/// </summary>
public class BaseModel
{public int Id { get; set; }//租户Idpublic int TId { get; set; }//是否删除（软删除）public bool IsDelete { get; set; }
}
/// <summary>
/// 员工类
/// </summary>
public class Employee:BaseModel
{public string Name { get; set; }public int Age { get; set; }public Department Department { get; set; }
}
/// <summary>
/// 部门类
/// </summary>
public class Department:BaseModel
{public string DepName { get; set; }public int EmployeeId { get; set; }
}

下面我们实现 Employee 和 Department 的模型映射：

public class EmployeeConfiguration : IEntityTypeConfiguration<Employee>
{public void Configure(EntityTypeBuilder<Employee> builder){builder.ToTable("Employee");builder.HasKey(p => p.Id);builder.Property(p => p.Name);builder.Property(p => p.IsDelete);builder.Property(p => p.Age);builder.HasQueryFilter(p => !p.IsDelete);}
}
public class DepartmentConfiguration : IEntityTypeConfiguration<Department>
{public void Configure(EntityTypeBuilder<Department> builder){builder.ToTable("Department");builder.HasKey(p => p.Id);builder.Property(p => p.DepName);builder.Property(p => p.IsDelete);builder.HasQueryFilter(p => !p.IsDelete);builder.HasMany(p => p.Employees).WithOne(e => e.Department).HasForeignKey(k => k.DepartmentId);}
}

接下来我们再定义一个多租户Id接口和实现，实现里的返回值是定死的，用来模拟检测与当前请求相关的租户。

public interface ITenantProvider
{int GetTId();
}
public class TenantProvider : ITenantProvider
{public int GetTId(){return 1;}
}

最后我们定义查询 Department 的接口和实现：

public interface IDepartmentDb
{IQueryable<Department> GetDepartments();
}
public class DepartmentDb : IDepartmentDb
{private EFContext ef;public DepartmentDb(EFContext _ef){ef = _ef;}public IQueryable<Department> GetDepartments(){var departments = ef.Departments;return departments;}
}

前提条件

public interface IEntityTypeProvider
{IEnumerable<Type> GetTypes();
}public class EntityTypeProvider : IEntityTypeProvider
{IList<Type> entityTypeCache;public IEnumerable<Type> GetTypes(){if(entityTypeCache!=null){return entityTypeCache.ToList();}entityTypeCache = (from a in GetReferencingAssemblies()from t in a.DefinedTypeswhere t.BaseType == typeof(BaseModel)select t.AsType()).ToList();return entityTypeCache;}private IEnumerable<Assembly> GetReferencingAssemblies(){var assemblies = new List<Assembly>();var dependencies = DependencyContext.Default.RuntimeLibraries;foreach (var library in dependencies){var assembly = Assembly.Load(new AssemblyName(library.Name));assemblies.Add(assembly);}return assemblies;}}

应用

public class EFContext : DbContext
{public DbSet<Employee> Employees;public DbSet<Department> Departments;protected override void OnModelCreating(ModelBuilder modelBuilder){modelBuilder.ApplyConfiguration(new EmployeeConfiguration());modelBuilder.ApplyConfiguration(new DepartmentConfiguration());base.OnModelCreating(modelBuilder);}private int tId;private IEntityTypeProvider entityTypeProvider;public EFContext(DbContextOptions<EFContext> options,ITenantProvider tenantProvider,IEntityTypeProvider entityTypeProvider):base(options){tId = tenantProvider.GetTId();this.entityTypeProvider = entityTypeProvider;}
}

第二步在上下文中定义全局查询过滤的泛型方法：

public void GlobalQuery<T> (ModelBuilder builder) where T :BaseModel
{builder.Entity<T>().HasQueryFilter(e => e.TId == tId && !e.IsDelete);
}

然后在上下文中获取设置全局查询过滤方法的 MethodInfo 类：

static readonly MethodInfo GlobalQueryMethod = typeof(EFContext).GetMethods(BindingFlags.Public | BindingFlags.Instance).Single(p=>p.IsGenericMethod && p.Name== "GlobalQuery");

最后，在OnModelCreating方法中，通过注入的 entityTypeProvider 获取需要全局查询过滤的类型集合，并进行遍历，调用得到进行查询过滤的方法传入 modelBuilder 参数，从而实现多租户查询过滤。

protected override void OnModelCreating(ModelBuilder modelBuilder)
{modelBuilder.ApplyConfiguration(new EmployeeConfiguration());modelBuilder.ApplyConfiguration(new DepartmentConfiguration());foreach (var item in entityTypeProvider.GetTypes()){var method = GlobalQueryMethod.MakeGenericMethod(item);method.Invoke(this, new object[] { modelBuilder });}base.OnModelCreating(modelBuilder);
}

总结

作者简介：朱钢，笔名喵叔，CSDN博客专家，.NET高级开发工程师，7年一线开发经验，参与过电子政务系统和AI客服系统的开发，以及互联网招聘网站的架构设计，目前就职于北京恒创融慧科技发展有限公司，从事企业级安全监控系统的开发。

声明：本文系作者独立观点，不代表CSDN立场。