EF 学习笔记

1、一次性添加映射

    public class EntityDbContext : DbContext 
    {  
        public EntityDbContext()
            : base("name=test2")
        { }


        /// <summary>
        /// 通过反射一次性将表进行映射
        /// </summary>
        /// <param name="modelBuilder"></param>
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
           
            var typesRegister = Assembly.GetExecutingAssembly().GetTypes()
                .Where(type => !(string.IsNullOrEmpty(type.Namespace))).Where(type => type.BaseType != null && type.BaseType.IsGenericType && type.BaseType.GetGenericTypeDefinition() == typeof(EntityTypeConfiguration<>));
            foreach (var type in typesRegister)
            {
                dynamic configurationInstance = Activator.CreateInstance(type);
                modelBuilder.Configurations.Add(configurationInstance);
            }

        }
    }

    public class StudentMap : EntityTypeConfiguration<Student>
    {
        public StudentMap()
        {
            ToTable("Student");
            HasKey(d => d.ID);
          
            //HasRequired(p => p.Course).WithRequiredDependent(i => i.Student);           
            //HasRequired(p => p.Course).WithOptional(i => i.Student);

            HasRequired(p => p.Course).WithRequiredPrincipal(p => p.Student);
            HasOptional(p => p.Course).WithRequired(p => p.Student);

            /*
             对于上述映射关系不太理解的话可以去上述给出链接文章。我只说明怎么去很好的理解这两组的意思，第一组 WithRequiredDependent 和第二组
             WithRequiredPrincipal 一个是Dependent是依赖的意思说明后面紧接着的Student是依赖对象，而前面的Course是主体，而Principal
             首先的意思，说明后面紧接着的是Student是主体，而Course是依赖对象。很显然在这个关系中课程是依赖学生的。所以映射选第二组  
            */
        }
    }

2、延迟加载必须满足三个条件：

1. this.Configuration.ProxyCreationEnabled = true;
2. this.Configuration.LazyLoadingEnabled = true;
3. 导航属性修饰符必须为Virtual

3、映射private/protected/internal属性：

    public class Student
    {
        public string Id { get; set; }
        public string Name { get; set; }
        private string TestPrivate { get; set; }
        internal string TestInternal { get; set; }
        protected string TestProtected { get; set; }
    ｝

　　public class BreakAwayContext : DbContext
    {
        public BreakAwayContext()
            : base("name=BreakAwayContext")
        {
            this.Configuration.LazyLoadingEnabled = false;//对所有实体关闭惰性加载
            this.Configuration.ProxyCreationEnabled = false;//禁止创建代理

            DbInterception.Add(new NLogCommandInterceptor());
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            ////<EF 6.0
            //modelBuilder.Entities().Configure(c =>
            //{
            //    var nonPublicProperties = c.ClrType.GetProperties(BindingFlags.NonPublic | BindingFlags.Instance);

            //    foreach (var p in nonPublicProperties)
            //    {
            //        c.Property(p).HasColumnName(p.Name);
            //    }
            //});
            //EF 6.0
            modelBuilder.Types().Configure(d =>
            {
                var nonPublicProperties = d.ClrType.GetProperties(BindingFlags.NonPublic | BindingFlags.Instance);
                foreach (var p in nonPublicProperties)
                {
                    d.Property(p).HasColumnName(p.Name);
                }
            });
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        }

        public DbSet<Student> Students { get; set; }

    }

4、各种查询：

条件查询

　　　　var sql = "select ID, Name, Age from Student where Name = @Name and Age = @Age";

 　　　 ctx.Database.SqlQuery<Student>(
                sql, 
                new SqlParameter("@Name", Name),
                new SqlParameter("@Age", Age));

非实体查询

ctx.Database.SqlQuery<int>("select Age from Student").ToList();

 执行存储过程

ctx.Database.SqlQuery<Student>("dbo.GetList").ToList();

 var param = new SqlParameter("Age", 5);
 var list = ctx.Database.SqlQuery<Student>("dbo.GetList @Age", param).ToList();

/*查询出的所有列必须对应返回实体中的所有字段，缺一不可，否则报错！在调用存储过程中，如果数据库是Sql 2005要在存储过程名称前加上 EXEC,否则报错*/

　　　　　　　var name = new SqlParameter { ParameterName = "Name", Value = Name };
            var currentpage = new SqlParameter { ParameterName = "PageIndex", Value = currentPage };
            var pagesize = new SqlParameter { ParameterName = "PageSize", Value = pageSize };
            var totalcount = new SqlParameter { ParameterName = "TotalCount", Value = 0, Direction = ParameterDirection.Output };

            var list = ctx.Database.SqlQuery<Student>("Myproc @Name, @PageIndex, @PageSize, @TotalCount output",
        name, currentpage, pagesize, totalcount);

            totalCount = (int)totalcount.Value;  /*获得要输出参数totalcount的值*/

public IList<TEntity> ExecuteStoredProcedureList<TEntity>(string commandText, params object[] parameters) where TEntity : class
        {
            if (parameters != null && parameters.Length > 0)
            {
                for (int i = 0; i <= parameters.Length - 1; i++)
                {
                    var p = parameters[i] as DbParameter;
                    if (p == null)
                        throw new Exception("Not support parameter type");

                    commandText += i == 0 ? " " : ", ";

                    commandText += "@" + p.ParameterName;
                    if (p.Direction == ParameterDirection.InputOutput || p.Direction == ParameterDirection.Output)
                    {

                        commandText += " output";
                    }
                }
            }

            var result = this.Database.SqlQuery<TEntity>(commandText, parameters).ToList();

 
            bool acd = this.Configuration.AutoDetectChangesEnabled;
            
            try
            {
                this.Configuration.AutoDetectChangesEnabled = false;

                for (int i = 0; i < result.Count; i++)
                    result[i] = this.Set<TEntity>().Attach(result[i]);
            }
            finally
            {
                this.Configuration.AutoDetectChangesEnabled = acd;
            }

            return result;
        }

var list = ctx.ExecuteStoredProcedureList<Student>("Myproc", pageindex, pagesize, totalcount);

5、EF在查询之前进行操作来忽略尾随空格

    public class EFConfiguration : DbConfiguration
    {
        public EFConfiguration()
        {
            AddInterceptor(new StringTrimmerInterceptor());
        }
    }
    public class StringTrimmerInterceptor : IDbCommandTreeInterceptor
    {
        public void TreeCreated(DbCommandTreeInterceptionContext interceptionContext)
        {
            if (interceptionContext.OriginalResult.DataSpace == DataSpace.SSpace)
            {
                var queryCommand = interceptionContext.Result as DbQueryCommandTree;
                if (queryCommand != null)
                {
                    var newQuery = queryCommand.Query.Accept(new StringTrimmerQueryVisitor());
                    interceptionContext.Result = new DbQueryCommandTree(
                        queryCommand.MetadataWorkspace,
                        queryCommand.DataSpace,
                        newQuery);
                }
            }
        }

        private class StringTrimmerQueryVisitor : DefaultExpressionVisitor
        {
            private static readonly string[] _typesToTrim = { "nvarchar", "varchar", "char", "nchar" };

            public override DbExpression Visit(DbNewInstanceExpression expression)
            {
                var arguments = expression.Arguments.Select(a =>
                {
                    var propertyArg = a as DbPropertyExpression;
                    if (propertyArg != null&& _typesToTrim.Contains(propertyArg.Property.TypeUsage.EdmType.Name))
                    {
                        return EdmFunctions.Trim(a);
                    }
 
                    return a;
                });
 
                return DbExpressionBuilder.New(expression.ResultType, arguments);
            }
        }
    }

6、扩展方法

    public static class EFExt
    {
        /// <summary>
        /// 获得实体的所有键的名称
        /// </summary>
        /// <param name="ctx"></param>
        /// <param name="entity"></param>
        /// <returns></returns>
        static string[] GetKeyNames(this DbContext ctx, Type entity)
        {
            var metadata = ((IObjectContextAdapter)ctx).ObjectContext.MetadataWorkspace;

            /*获得CLR type集合和medata OSpace之间的映射*/
            var objItemCollection = (ObjectItemCollection)metadata.GetItemCollection(DataSpace.OSpace);

            /*根据所给的CLR type获得实体的元数据即metadata*/
            var entitydata = metadata.GetItems<EntityType>(DataSpace.OSpace).Single(e => objItemCollection.GetClrType(e) == entity);
            /*返回实体的所有键的集合*/
            return entitydata.KeyProperties.Select(p => p.Name).ToArray();

        }
        /// <summary>
        /// 获得实体对应的表名
        /// </summary>
        /// <param name="ctx"></param>
        /// <param name="entity"></param>
        /// <returns></returns>
        static string GetTableName(this DbContext ctx, Type entity)
        {
            var metadata = ((IObjectContextAdapter)ctx).ObjectContext.MetadataWorkspace;

            var storeItemCollection = metadata.GetItemCollection(DataSpace.SSpace);

            var entitySetBase = storeItemCollection.GetItems<EntityContainer>().Single().BaseEntitySets.Where(e => e.Name == entity.Name).Single();

            string tableName = entitySetBase.MetadataProperties["Schema"].Value + "." + entitySetBase.MetadataProperties["Table"].Value;

            return tableName;
        }
        /// <summary>
        /// 获得实体的所有导航属性
        /// </summary>
        /// <param name="ctx"></param>
        /// <param name="entity"></param>
        /// <returns></returns>
        static IEnumerable<PropertyInfo> GetNavigationPrpoperties(this DbContext ctx, Type entity)
        {
            var metadata = ((IObjectContextAdapter)ctx).ObjectContext.MetadataWorkspace;

            var entityType = metadata.GetItems(DataSpace.OSpace).Where(d => d.BuiltInTypeKind == BuiltInTypeKind.EntityType).OfType<EntityType>().Where(d => d.Name == entity.Name).Single();

            return (entityType.NavigationProperties.Select(d => entity.GetProperty(d.Name)).ToList());

        }
    }

 7、二级缓存【参考官方Second Level Cace for EntityFramework】

　　public class EFConfiguration : DbConfiguration
    {
        public EFConfiguration()
        {
            var transactionHandler = new CacheTransactionHandler(new InMemoryCache());

            AddInterceptor(transactionHandler);

            var cachingPolicy = new CachingPolicy();

            Loaded +=
             (sender, args) => args.ReplaceService<DbProviderServices>(
             (s, _) => new CachingProviderServices(s, transactionHandler,
              cachingPolicy));

        }

    }