Common Relationship Operators


In this chapter, we will discuss about the operators which build on relationships.

__eq__()

The above operator is a many-to-one “equals” comparison. The line of code for this operator is as shown below −

s = session.query(Customer).filter(Invoice.invno.__eq__(12))

The equivalent SQL query for the above line of code is −

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

__ne__()

This operator is a many-to-one “not equals” comparison. The line of code for this operator is as shown below −

s = session.query(Customer).filter(Invoice.custid.__ne__(2))

The equivalent SQL query for the above line of code is given below −

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

contains()

This operator is used for one-to-many collections and given below is the code for contains() −

s = session.query(Invoice).filter(Invoice.invno.contains([3,4,5]))

The equivalent SQL query for the above line of code is −

SELECT invoices.id 
AS invoices_id, invoices.custid 
AS invoices_custid, invoices.invno 
AS invoices_invno, invoices.amount 
AS invoices_amount
FROM invoices
WHERE (invoices.invno LIKE '%' + ? || '%')

any()

any() operator is used for collections as shown below −

s = session.query(Customer).filter(Customer.invoices.any(Invoice.invno==11))

The equivalent SQL query for the above line of code is shown below −

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers
WHERE EXISTS (
   SELECT 1
   FROM invoices
   WHERE customers.id = invoices.custid 
   AND invoices.invno = ?)

has()

This operator is used for scalar references as follows −

s = session.query(Invoice).filter(Invoice.customer.has(name = 'Arjun Pandit'))

The equivalent SQL query for the above line of code is −

SELECT invoices.id 
AS invoices_id, invoices.custid 
AS invoices_custid, invoices.invno 
AS invoices_invno, invoices.amount 
AS invoices_amount
FROM invoices
WHERE EXISTS (
   SELECT 1
   FROM customers
   WHERE customers.id = invoices.custid 
   AND customers.name = ?)
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