Database Reference
In-Depth Information
Since this is such a common use case, many relational database systems provide cascading
constraints in the table-creation logic that do this automatically. For instance, we may have
designed our tables using the following SQL:
CREATE
CREATE TABLE
TABLE
`
orders
`
(
`
id
`
CHAR
(
5
)
NOT
NOT NULL
NULL
,
...
PRIMARY
PRIMARY KEY
KEY
(
`
id
`
))
CREATE
CREATE TABLE
TABLE
`
order_items
`
(
`
order_id
`
CHAR
(
5
)
NOT
NOT NULL
NULL
,
`
sku
`
CHAR
(
8
)
NOT
NOT NULL
NULL
,
...
PRIMARY
PRIMARY KEY
KEY
(
`
order_id
`
,
`
sku
`
),
FOREIGN
FOREIGN KEY
KEY
(
`
order_id
`
)
REFERENCES
REFERENCES
orders
.
id
OON DELETE
DELETE CASCADE
CASCADE
)
In this case, we could execute a simpler SQL statement:
DELETE
DELETE FROM
FROM
orders
WHERE
WHERE
id
=
'11223'
;
However, despite the fact that we're not explicitly calling
BEGIN
and
COMMIT
, the database
system is still doing the work of a full, multitable transaction.
A developer new to MongoDB may approach an order management system by designing a
relational-style schema:
// "orders" document
{
_id
:
'11223'
,
...
}
// "order_items" document
{
_id
:
ObjectId
(...),
order_id
:
'11223'
,
sku
:
'...'
,
...
}
