python，web编程（二）
写好web基本骨架以后，开始编写数据库的orm存放到orm.py文件中，才疏学浅有些地方还不是很理解，先上代码吧：
#创建连接池 @asyncio.coroutine def create_pool(loop, **kw): logging.info('create database connection pool...') global __pool __pool = yield from aiomysql.create_pool( host=kw.get('host','localhost'), port=kw.get('port',3306), user=kw['root'], password=kw['root'], db=kw['db'], charset=kw.get('charset','utf8'), autocommit=kw.get('autocommit',True), maxsize=kw.get('maxsize',10), minsize=kw.get('minsize',1), loop=loop )
首先创建连接池，这个很好理解，因为每次对数据库操作都需要连接数据库，直接用一个全局变量来创建数据库连接这样更方便。
定义select语句：
@asyncio.coroutine def select(sql,args,size=None): log(sql,args) global __pool with (yield from __pool) as conn: cur = yield from conn.cursor(aiomysql.DictCursor) yield from cur.execute(sql,replace('?','%s'), args or ()) if size: rs = yield from cur.fetchmany(size) else: rs = yield from cur.fetchall() yield from cur.close() logging.info('rows returned:%s' % len(rs)) return rs
定义update，delete，insert语句，因为这3个语句的参数是一样的，所以可以用一个函数去定义它们：
@asyncio.coroutine def execute(sql, args): log(sql) with (yield from __pool) as conn: try: cur = yield from conn.cursor() yield from cur.execute(sql.replace('?','%s'),args) affected = cur.rowcount yield from cur.close() except BaseException as e: raise return affected
接下来要编写基类Model类，所有的表类都是继承这个基类的，先编写基类的元类，这里我也不是很明白，姑且记录下来自己的理解：
#定义Model类的原类 class ModelMetaclass(type): def __new__(cls, name, bases, attrs): #排除Model类本身 if name=='Model': return type.__new__(cls, name, bases, attrs) #获取table名称 tableName = attrs.get('__table__', None) or name logging.info('found model: %s (table: %s)' % (name, tableName)) #获取所有的Field和主键名 mappings = dict() fields = [] primaryKey = None for k, v in attrs.items(): if isinstance(v,Field): logging.info(' found mapping:%s ==> %s' % (k, v)) mappings[k] = v if v.primary_key: #找到主键 if primaryKey: raise RuntimeError('Duplicate primary key for field: %s' % k) primaryKey = k else: fields.append(k) if not primaryKey: raise RuntimeError('Primary key not found.') for k in mappings.keys(): attrs.pop(k) escaped_fields = list(map(lambda f: '%s' % f,fields)) attrs['__mappings__'] = mappings #保存属性和列的映射关系 attrs['__table__'] = tableName attrs['__primary_key__'] = primaryKey #主键属性名 attrs['__fields__'] = fields # 除主键外的属性名 # 构造默认的SELECT, INSERT, UPDATE和DELETE语句: attrs['__select__'] = 'select `%s`, %s from `%s`' % (primaryKey, ', '.join(escaped_fields), tableName) attrs['__insert__'] = 'insert into `%s` (%s, `%s`) values (%s)' % (tableName, ', '.join(escaped_fields), primaryKey, create_args_string(len(escaped_fields) + 1)) attrs['__update__'] = 'update `%s` set %s where `%s`=?' % (tableName, ', '.join(map(lambda f: '`%s`=?' % (mappings.get(f).name or f), fields)), primaryKey) attrs['__delete__'] = 'delete from `%s` where `%s`=?' % (tableName, primaryKey) return type.__new__(cls, name, bases, attrs)
元类就是定义类的类，可以认为类是该元类的一个实例__new__方法为类的构造方法cls为元类的实例，所有继承model类的类都会拥有元类的方法。元类定义了一个__table__属性，它的值由参数name决定，即类实例的名字。通过类的__mappings__属性保存了列和数据表字段的映射关系（这里不理解）。同理 后面设定了select insert update delete的构造语句。这些当类创建的时候，就拥有这些熟悉了。
之后定义Model类：
#编写基类Model class Model(dict, metaclass=ModelMetaclass): def __init__(self,**kw): super(Model, self),__init__(**kw) def __getattr__(self, key): try: return self[key] except KeyError: raise AttributeError(r"'Model' object has no attribute '%s'" % key) def __setattr__(self, key, value): self[key] = value def getValue(self, key): return getattr(self, key, None) def getValueOrDefault(self, key): value = getattr(self, key, None) if value is None: field = self.__mappings__[key] if field.default is not None: value = field.default() if callable(field.default) else field.default logging.debug('using default value for %s: %s' % (key,str(value))) setattr(self, key, value) return value @classmethod @asyncio.coroutine def find(cls, pk): 'find object by primary key.' rs = yield from select('%s where %s =?' % (cls.__select__,cls.__primary_key__),[pk], 1) if len(rs) == 0: return None return cls(**rs[0]) @classmethod @asyncio.coroutine def findAll(cls, where=None, args=None, **kw): 'find objects by where clause.' sql = [cls.__select__] if where: sql.append('where') sql.append(where) if args is None: args = [] orderBy = kw.get('orderBy', None) if orderBy: sql.append('order by') sql.append(orderBy) limit = kw.get('limit', None) if limit is not None: sql.append('limit') if isinstance(limit, int): sql.append('?') args.append(limit) elif isinstance(limit, tuple) and len(limit) == 2: sql.append('?,?') args.extend(limit) else: raise ValueError('Invalid limit value: %s' % str(limit)) rs = yield from select(' '.join(sql), args) return [cls(**r) for r in rs] @classmethod @asyncio.coroutine def findNumber(cls, selectField, where=None, args=None): 'find number by select and where.' sql = ['select %s _num_ from %s' % (selectField, cls.__table__)] if where: sql.append('where') sql.append(where) rs = yield from select(' '.join(sql), args, 1) if len(rs) == 0: return None return rs[0]['_num_'] @classmethod @asyncio.coroutine def save(self): args = list(map(self.getValueOrDefault,self.__fields__)) args.append(self.getValueOrDefault(self.__primary_key__)) rows = yield from execute(self.__insert__, args) if rows !=1: logging.warn('failed to insert record: affected rows: %s' % rows) @asyncio.coroutine def update(self): args = list(map(self.getValue,self.__fields__)) args.append(self.getValue(self.__primary_key__)) rows = yield from execute(self.__update__, args) if rows != 1: logging.warn('failed to update by primary key: affected rows: %s' % rows) @asyncio.coroutine def remove(self): args = [self.getValue(self.__primary_key__)] rows = yield from execute(self.__delete__, args) if rows != 1: logging.warn('failed to remove by primary key: affected rows: %s' % rows)
基类继承了python的dict类，元类为之前定义的，然后通过这些定义了基本的数据库操作。之后便是定义Field类和各个子类，这些都是字段的类型：
#定义Field类 class Field(object): def __init__(self, name, column_type,primary_key, default): self.name = name self.column_type = column_type self.primary_key = primary_key self.default = default def __str__(self): return '<%s, %s:%s>' % (self.__class__.__name__,self.column_type,self.name) #映射varchar的StringField类 class StringField(Field): def __init__(self, name=None, primary_key=False, default=None, ddl='varchar(100)'): super().__init__(name, ddl, primary_key, default)
一个orm就编写完成了
