【.Net】使用配置文件 DbContext 动态加载 DbSet

1、配置文件中定义节点，可根据 自己的情况更改节点或属性

<configuration> 
 <CustomAssemblySection>
    <assemblies>
      <add name="Seven.Core.Models"></add>
    </assemblies>
  </CustomAssemblySection>
</configuration>

2、自定义配置文件的节点，继承ConfigurationSection

public class CustomAssemblySection : ConfigurationSection
    {
        [ConfigurationProperty("assemblies", IsDefaultCollection = false)]
        [ConfigurationCollection(typeof(CustomAssemblyCollection))]
        public CustomAssemblyCollection Assemblies
        {
            get
            {
                return (CustomAssemblyCollection)base["assemblies"];
            }
        }
    }　　

3、自定配置子节点，继承ConfigurationElementCollection

 public class CustomAssemblyCollection : ConfigurationElementCollection
    {
        protected override ConfigurationElement CreateNewElement()
        {
            return new CustomAssemblyElement();
        }

        protected override object GetElementKey(ConfigurationElement element)
        {
            return ((CustomAssemblyElement)element).Name;
        }

        public CustomAssemblyElement this[int Index]
        {
            get
            {
                return (CustomAssemblyElement)BaseGet(Index);
            }

            set
            {
                if (BaseGet(Index) != null)
                {
                    BaseRemoveAt(Index);
                }
                BaseAdd(Index, value);
            }
        }

        new public CustomAssemblyElement this[string Name]
        {
            get
            {
                return (CustomAssemblyElement)BaseGet(Name);
            }
        }
    }

4、配置属性名称

public class CustomAssemblyElement : ConfigurationElement
    {
        [ConfigurationProperty("name", IsRequired = true)]
        public string Name
        {
            get
            {
                return (string)this["name"];
            }
            set
            {
                this["name"] = value;
            }
        }
    }

5、在配置文件中配置，CustomAssemblySeciton为自定义，type填写定义的程序集

<configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    <section name="CustomAssemblySection" type=" Seven.Component.Data.EntityAssist.CustomAssemblySection,Seven.Component.Data"/>
  </configSections>

6、重写Contenxt中的OnModelCreating方法（以下代码判断是否有Table属性的进行反射，可根据自己情况定义）

[Export("EF", typeof(DbContext))]
    public class EFDbContext : DbContext
    {
        public EFDbContext()
            : base("MSDBContext") {
            EntityMappers = GetEntityMappers();
        }

        public EFDbContext(string nameOrConnectionString)
           : base(nameOrConnectionString) {
            EntityMappers = GetEntityMappers();
        }

        public EFDbContext(DbConnection existingConnection)
            : base(existingConnection, true) {
            EntityMappers = GetEntityMappers();
        }

        private static List<Type> EntityMappers { get; set; }

        private static List<Type> GetEntityMappers()
        {
            List<Type> types = new List<Type>();

            CustomAssemblySection configSection = (CustomAssemblySection)System.Configuration.ConfigurationManager.GetSection("CustomAssemblySection");
            foreach (CustomAssemblyElement customAssembly in configSection.Assemblies)
            {
                Assembly assembly = Assembly.Load(customAssembly.Name);
                foreach (Type type in assembly.ExportedTypes)
                {
                    if (!type.IsClass) continue;

                    var tableattrd = type.GetCustomAttribute(typeof(TableAttribute));
                    if (tableattrd != null)
                    {
                        types.Add(type);
                    }
                }
            }

            return types;
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            foreach(var type in EntityMappers)
            {
                MethodInfo method = modelBuilder.GetType().GetMethod("Entity");
                method = method.MakeGenericMethod(new Type[] { type });
                method.Invoke(modelBuilder, null);
            }

            base.OnModelCreating(modelBuilder);
        }
    }