SQLAlchemy ORM - 过滤操作符

现在，我们将学习过滤操作及其相应的代码和输出。

等于

常用的操作符是 ==，它应用条件来检查相等性。

result = session.query(Customers).filter(Customers.id == 2)

for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

SQLAlchemy 将发送以下 SQL 表达式：

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.id = ?

以上代码的输出如下：

ID: 2 Name: Komal Pande Address: Banjara Hills Secunderabad Email: komal@gmail.com

不等于

不等于的操作符是 !=，它提供不等于条件。

result = session.query(Customers).filter(Customers.id! = 2)

for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

生成的 SQL 表达式为：

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.id != ?

以上代码行的输出如下：

ID: 1 Name: Ravi Kumar Address: Station Road Nanded Email: ravi@gmail.com
ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com
ID: 4 Name: S.M.Krishna Address: Budhwar Peth, Pune Email: smk@gmail.com

LIKE

like() 方法本身会为 SELECT 表达式中的 WHERE 子句生成 LIKE 条件。

result = session.query(Customers).filter(Customers.name.like('Ra%'))
for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

以上 SQLAlchemy 代码等效于以下 SQL 表达式：

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.name LIKE ?

以上代码的输出为：

ID: 1 Name: Ravi Kumar Address: Station Road Nanded Email: ravi@gmail.com
ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com

IN

此操作符检查列值是否属于列表中的一组项目。它由 in_() 方法提供。

result = session.query(Customers).filter(Customers.id.in_([1,3]))
for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

这里，SQLite 引擎评估的 SQL 表达式如下：

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.id IN (?, ?)

以上代码的输出如下：

ID: 1 Name: Ravi Kumar Address: Station Road Nanded Email: ravi@gmail.com
ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com

AND

此连接词可以通过 **在过滤器中放置多个逗号分隔的条件或使用 and_() 方法** 生成，如下所示：

result = session.query(Customers).filter(Customers.id>2, Customers.name.like('Ra%'))
for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

from sqlalchemy import and_
result = session.query(Customers).filter(and_(Customers.id>2, Customers.name.like('Ra%')))

for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

以上两种方法都会产生类似的 SQL 表达式：

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.id > ? AND customers.name LIKE ?

以上代码行的输出为：

ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com

OR

此连接词由 **or_() 方法** 实现。

from sqlalchemy import or_
result = session.query(Customers).filter(or_(Customers.id>2, Customers.name.like('Ra%')))

for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

结果，SQLite 引擎获得以下等效的 SQL 表达式：

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE customers.id > ? OR customers.name LIKE ?

以上代码的输出如下：

ID: 1 Name: Ravi Kumar Address: Station Road Nanded Email: ravi@gmail.com
ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com
ID: 4 Name: S.M.Krishna Address: Budhwar Peth, Pune Email: smk@gmail.com

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