Castle ActiveRecord学习实践(2)映射

本文将介绍Castle ActiveRecord 中的基本映射。

    [ActiveRecord("Posts")]
    public class Post:ActiveRecordBase<Post>
    {
        [PrimaryKey("PostId")]
        public int Id { get; set; }

        [Property]
        public string Subject { get; set; }

        [Property]
        public string Text { get; set; }

        [Property]
        public DateTime DateAdded { get; set; }

        [HasMany]
        public IList<Comment> Comments { get; set; }
        个o

    }

上面的的代码中已经包含了部分特性（ActiveRecord、Property、PrimaryKey、HasMany），这些特性类在Castle.ActiveRecord 命名空间中。主要的有

ActiveRecordAttribute

PropertyAttribute

PrimaryKeyAttribute

CompositeKeyAttribute

FieldAttribute

ActiveRecordAttribute

每一个实体类都必须继承于ActiveRecordBase，并在实体类上设置特性ActiveRecordAttribute

ActiveRecordAttribute的成员

属性	类型	说明	示例
BatchSize	int	为获取此类的实例标识符指定"批处理大小"
DiscriminatorColumn	string	识别器的字段名	DiscriminatorColumn="Post"
DiscriminatorLength	string	识别器的长度
DiscriminatorType	string	识别器的字段类型（int、string）	DiscriminatorType=”string”
DiscriminatorValue	string	识别器字段的值
DynamicInsert	bool	From NHibernate documentation: Specifies that INSERT SQL should be generated at runtime and contain only the columns whose values are not null. 如果没有对成员变量赋值，直接调用SAVE方法的话，SQL字段中允许为NULL的字段就可以由sql赋予其默认值。因为如果不是可以为Null的话，nhibernate直接会给你个异常，告诉你有notnull字段没有初始化
DynamicUpdate	bool	From NHibernate documentation: Specifies that UPDATE SQL should be generated at runtime and contain only those columns whose values have changed.
Lazy	bool	Enable lazy loading for the type 指定是否延迟加载
LazySpecified	bool	Gets a value indicating whether explicit lazy behavior was specified. If explicit lazy behavior was not specified, it goes to the configuration to decide if the type should be lazy or not
Locking	Castle.ActiveRecord.OptimisticLocking	From NHibernate documentation: Determines the optimistic locking strategy. 确定乐观的锁定策略
Mutable	bool	From NHibernate documentation: Specifies that instances of the class are (not) mutable 指定类的实例 （不） 是可变
Persister	System.Type	From NHibernate documentation: Specifies a custom IEntityPersister.
Polymorphism	Castle.ActiveRecord.Polymorphism	From NHibernate documentation: Determines whether implicit or explicit query polymorphism is used.
Proxy	System.Type	From NHibernate documentation: Determines whether implicit or explicit query polymorphism is used. 指定一个接口，在延迟装载时作为代理使用
Schema	string	Gets or sets the schema name associated with the type 设置概要的信息
SchemaAction	string
SelectBeforeUpdate	bool	From NHibernate documentation: Specifies that NHibernate should never perform an SQL UPDATE unless it is certain that an object is actually modified. In certain cases (actually, only when a transient object has been associated with a new session using update()), this means that NHibernate will perform an extra SQL SELECT to determine if an UPDATE is actually required. 指定 NHibernate 应该永远不会执行 SQL 更新，除非它是某些对象实际修改。在某些情况下 （其实，只有当瞬态对象已经与使用 update()) 新会话相关联，这意味着 NHibernate 将执行额外 SQL SELECT 来确定是否确实需要更新。
Table	string	Gets or sets the table name associated with the type 表名，类名与表名相同可为空	[ActiveRecord("Posts")] [ActiveRecord(Table=" Posts ")]
Tuplizer	System.Type
UseAutoImport	bool	From NHibernate documentation: The auto-import attribute lets us use unqualified class names in the query language, by default. The assembly and namespace attributes specify the assembly where persistent classes are located and the namespace they are declared in. 自动导入属性允许我们在查询语言中，默认情况下使用非限定的类名。程序集和命名空间的属性指定持久性类所在的程序集和命名空间中声明它们。
Where	string	SQL condition to retrieve objects 指定一个附加SQL的WHERE子句

PropertyAttribute

在ActiveRecord中通过PropertyAttribute 来指定实体类属性有数据库表中的字段映射

属性	类型	说明	示例
Check	string	From NHibernate documentation: create an SQL check constraint on either column or table 约束
Column	string	Gets or sets the column name 设置字段名	Property("PostId")
ColumnType	string	Gets or sets the type of the column. 设置字段类型
Default	string
Formula	string	Gets or sets the formula used to calculate this property 一个SQL表达式，定义了这个计算（computed） 属性的值。计算属性没有和它对应的数据库字段。
Index	string	From NHibernate documentation: specifies the name of a (multi-column) index 指定 （多列） 的索引的名称
Insert	bool	Set to false to ignore this property when inserting entities of this ActiveRecord class. 表明在用于INSERT的SQL语句中是否包含这个字段。默认为true
IsOverride	bool
Lazy	bool
Length	int	Gets or sets the length of the property (for strings - nvarchar(50) ) 字段长度
NotNull	bool	Gets or sets a value indicating whether this property allow null. 是否允许为空
SqlType	string	From NHibernate documentation: overrides the default column type 重写默认的字段类型．
Unique	bool	Gets or sets a value indicating whether this PropertyAttribute is unique. 是否允许重复．
UniqueKey	string	From NHibernate documentation: A unique-key attribute can be used to group columns in a single unit key constraint.
Update	bool	Set to false to ignore this property when updating entities of this ActiveRecord class. 表明在用于UPDATE的SQL语句中是否包含这个字段。默认为true

PrimaryKeyAttribute

在实体类中，通过PrimaryKeyAttribute来指定表的主键

属性	类型	说明	示例
Column	string	Gets or sets the column name 设置字段名	PrimaryKey("PostId")
ColumnType	string	Gets or sets the type of the column. 设置字段类型
CustomGenerator	System.Type	Gets or sets the custom generator. The generator must implement IIdentifierGenerator 设置一个自定义的生成器．这个生成器必要实现IIdentifierGenerator接口
Generator	Castle.ActiveRecord.PrimaryKeyType	Gets or sets the generator. 设置一个生成器，是一个.NET类的名字，用来为该持久化类的实例生成惟一的标识．
IsOverride	bool
Length	int	Gets or sets the length of values in the column 设置字段长度
Params	string	Comma separated value of parameters to the generator 用parameters来为生成器配置参数或者初始化参数．
SequenceName	string	Gets or sets the name of the sequence. 当指定主键的生成方式为Sequence时，序列的名称 当指定主键的生成方式为Sequence时，Sequence的名称．	PrimaryKey(PrimaryKeyType.Sequence, SequenceName="myseqname")
UnsavedValue	string	Gets or sets the unsaved value. 设置该实例未保存时的值

PrimaryKeyType 主键生成方式的枚举

名称	说明
Assigned	The primary key value is always assigned. Note: using this you will lose the ability to call Save(), and will need to call Create() or Update() explicitly. 让应用程序在自己为对象分配一个标示符。
Counter	Returns a Int64 constructed from the system time and a counter value. 返回一个INT64类型的系统时间和一个记数器值．
Custom	A custom generator will be provided. See CustomGenerator
Foreign	This is a foreign key to another table 外键
Guid	Generate a Guid for the primary key Note: You should prefer using GuidComb over this value. 用一个新的System.Guid 作为标识符。
GuidComb	Generate a Guid in sequence, so it will have better insert performance in the DB. 用Jimmy Nilsso的一个算法产生一个新的System.Guid。
HiLo	Use the HiLo algorithm to get the next value  高低位,使用一个高/低位算法来高效的生成Int64, Int32 或者 Int16类型的标识符。
Identity	Use Identity column (auto number) Note: This force an immediate call to the DB when Create() is called 对DB2,MySQL, MS SQL Server, Sybase和HypersonicSQL的内置标识字段提供支持，生成自增的整型 当Create() 方法执行时，便会触发数据库表自增类型字段自增．
Increment	Returns a Int64, constructed by counting from the maximum primary key value at startup. 主键最大值加１
Native	Use an identity or sequence if supported by the database, otherwise, use the HiLo algorithm 根据底层数据库的能力选择 identity, sequence 或者 hilo中的一个。默认值。
SeqHiLo	Use a sequence and a HiLo algorithm - better performance on Oracle 使用序列的高低位,使用一个高/低位算法来高效的生成Int64, Int32 或者 Int16类型的标识符，给定一个数据库序列（sequence)的名字。
Sequence	Use a sequence 序列
UuidHex	Use the hex representation of a unique identifier 用一个System.Guid和它的ToString(string format)方法生成字符串类型的标识符。
UuidString	Use the string representation of a unique identifier 用一个新的System.Guid产生一个byte[] ，把它转换成字符串。

CompositeKeyAttribute

组合键比较麻烦，这里还是准备了个demo

和前面的博客差不多，新建表Tags TagPost

Post 类

    [ActiveRecord("Posts")]
    public class Post : ActiveRecordBase<Post>
    {
        [PrimaryKey("PostId")]
        public int Id { get; set; }

        [Property]
        public string Subject { get; set; }

        [Property]
        public string Text { get; set; }

        [Property]
        public DateTime DateAdded { get; set; }

        [BelongsTo("CategoryId")]
        public Category Category { get; set; }

        [HasMany]
        public IList<Comment> Comments { get; set; }

        [HasAndBelongsToMany(typeof(Tag), Table = "TagPost", ColumnKey = "PostId", ColumnRef = "TagId")]
        public IList<Tag> Tag { get; set; }

    }

主要的部分

[HasAndBelongsToMany(typeof(Tag), Table = "TagPost", ColumnKey = "PostId", ColumnRef = "TagId")]
public IList<Tag> Tag { get; set; }

表达tag表与TagPost的关系

Tag类

    [ActiveRecord("Tags")]
    public class Tag : ActiveRecordBase<Tag>
    {
        [PrimaryKey("TagId")]
        public int Id { get; set; }

        [Property("Tag")]
        public string TagName { get; set; }

        [HasAndBelongsToMany(typeof(Post), Table = "TagPost", ColumnKey = "TagId", ColumnRef = "PostId")]
        public IList<Post> Post { get; set; }
    }

与上面的Post类相同 10-12 行代码表示的  Post表与TagPost的关系

使用组合键作为主键，需要自定义一个类来作为主键属性的类型。

新建类 TagPostKey

    [Serializable]
    public class TagPostKey
    {
        [KeyProperty]
        public int PostId { get; set; }
        [KeyProperty]
        public int TagId { get; set; }

        public override int GetHashCode()
        {
            return TagId ^ PostId;
        }

        public override string ToString()
        {

            return string.Join(":", new string[] { PostId.ToString(), TagId.ToString() });
        }
        public override bool Equals(object obj)
        {
            if (this==obj)
            {
                return true;
            }
            TagPostKey key = obj as TagPostKey;
            if (key==null)
            {
                return false;
            }
            if (PostId!=key.PostId||TagId!=key.TagId)
            {
                return false;
            }
            return true;
        }
    }

注意 该类必须能够序列化，还需重写Equals和GetHashCode方法

TagPost类

    [ActiveRecord]
    public class TagPost:ActiveRecordBase<TagPost>
    {
        [CompositeKey]
        public TagPostKey Id { get; set; }

    }

FieldAttribute

在ActiveRecord中，允许我们直接对Field进行映射，使用FieldAttribute

    [ActiveRecord]
    public class TagPost:ActiveRecordBase<TagPost>
    {
        [CompositeKey]
        public TagPostKey Id { get; set; }


        [Field("ArbitraryValue")]
        int _arbitraryValue;
    }