Peewee 简明教程

Peewee - Query Builder

Peewee 还提供一个非 ORM API 来访问数据库。我们可以将数据库表和列绑定到 Peewee 中定义的 Table 和 Column 对象，而不是定义模型和字段，并使用它们来执行查询。

Peewee also provides a non-ORM API to access the databases. Instead of defining models and fields, we can bind the database tables and columns to Table and Column objects defined in Peewee and execute queries with their help.

首先，声明一个与数据库中的表对应的 Table 对象。你必须指定表名和列的列表。还可以选择提供主键。

To begin with, declare a Table object corresponding to the one in our database. You have to specify table name and list of columns. Optionally, a primary key can also be provided.

Contacts=Table('Contacts', ('id', 'RollNo', 'Name', 'City'))

这个表对象通过 bind() 方法与数据库绑定。

This table object is bound with the database with bind() method.

Contacts=Contacts.bind(db)

Example

现在，我们可以在这个表对象上使用 select() 方法设置一个 SELECT 查询，并迭代结果集，如下所示：

Now, we can set up a SELECT query on this table object with select() method and iterate over the resultset as follows −

names=Contacts.select()
for name in names:
   print (name)

Output

默认情况下，行以字典的形式返回。

The rows are by default returned as dictionaries.

{'id': 1,  'RollNo': 101, 'Name': 'Anil', 'City': 'Mumbai'}
{'id': 2,  'RollNo': 102, 'Name': 'Amar', 'City': 'Delhi'}
{'id': 3,  'RollNo': 103, 'Name': 'Raam', 'City': 'Indore'}
{'id': 4,  'RollNo': 104, 'Name': 'Leena', 'City': 'Nasik'}
{'id': 5,  'RollNo': 105, 'Name': 'Keshav', 'City': 'Pune'}
{'id': 6,  'RollNo': 106, 'Name': 'Hema', 'City': 'Nagpur'}
{'id': 7,  'RollNo': 107, 'Name': 'Beena', 'City': 'Chennai'}
{'id': 8,  'RollNo': 108, 'Name': 'John', 'City': 'Delhi'}
{'id': 9,  'RollNo': 109, 'Name': 'Jaya', 'City': 'Nasik'}
{'id': 10, 'RollNo': 110, 'Name': 'Raja', 'City': 'Nasik'}

如果需要的话，它们可以作为元组、命名元组或对象获取。

If needed, they can be obtained as tuples, namedtuples or objects.

Tuples

程序如下：

The program is as follows −

Example

names=Contacts.select().tuples()
for name in names:
   print (name)

Output

输出如下 −

The output is given below −

(1, 101, 'Anil', 'Mumbai')
(2, 102, 'Amar', 'Delhi')
(3, 103, 'Raam', 'Indore')
(4, 104, 'Leena', 'Nasik')
(5, 105, 'Keshav', 'Pune')
(6, 106, 'Hema', 'Nagpur')
(7, 107, 'Beena', 'Chennai')
(8, 108, 'John', 'Delhi')
(9, 109, 'Jaya', 'Nasik')
(10, 110, 'Raja', 'Nasik')

Namedtuples

程序如下：

The program is stated below −

Example

names=Contacts.select().namedtuples()
for name in names:
   print (name)

Output

输出如下 −

The output is given below −

Row(id=1, RollNo=101, Name='Anil', City='Mumbai')
Row(id=2, RollNo=102, Name='Amar', City='Delhi')
Row(id=3, RollNo=103, Name='Raam', City='Indore')
Row(id=4, RollNo=104, Name='Leena', City='Nasik')
Row(id=5, RollNo=105, Name='Keshav', City='Pune')
Row(id=6, RollNo=106, Name='Hema', City='Nagpur')
Row(id=7, RollNo=107, Name='Beena', City='Chennai')
Row(id=8, RollNo=108, Name='John', City='Delhi')
Row(id=9, RollNo=109, Name='Jaya', City='Nasik')
Row(id=10, RollNo=110, Name='Raja', City='Nasik')

要插入一条新记录，INSERT 查询的构建如下所示：

To insert a new record, INSERT query is constructed as follows −

id = Contacts.insert(RollNo=111, Name='Abdul', City='Surat').execute()

如果要添加的记录列表存储为字典列表或元组列表，则可以批量添加它们。

If a list of records to be added is stored either as a list of dictionaries or as list of tuples, they can be added in bulk.

Records=[{‘RollNo’:112, ‘Name’:’Ajay’, ‘City’:’Mysore’},
   {‘RollNo’:113, ‘Name’:’Majid’,’City’:’Delhi’}}

Or

Records=[(112, ‘Ajay’,’Mysore’), (113, ‘Majid’, ‘Delhi’)}

INSERT 查询的编写方式如下：

The INSERT query is written as follows −

Contacts.insert(Records).execute()

Peewee Table 对象有 update() 方法来实现 SQL UPDATE 查询。要将 Nasik 中所有记录的 City 更改为 Nagar，我们使用以下查询。

The Peewee Table object has update() method to implement SQL UPDATE query. To change City for all records from Nasik to Nagar, we use following query.

Contacts.update(City='Nagar').where((Contacts.City=='Nasik')).execute()

最后，Peewee 中的 Table 类还有 delete() 方法来实现 SQL 中的 DELETE 查询。

Finally, Table class in Peewee also has delete() method to implement DELETE query in SQL.

Contacts.delete().where(Contacts.Name=='Abdul').execute()