mirror of https://gitee.com/bigwinds/arangodb
51 lines
1.2 KiB
Plaintext
51 lines
1.2 KiB
Plaintext
!CHAPTER LET
|
|
|
|
The *LET* statement can be used to assign an arbitrary value to a variable. The
|
|
variable is then introduced in the scope the *LET* statement is placed in. The
|
|
general syntax is:
|
|
|
|
```
|
|
LET variable-name = expression
|
|
```
|
|
|
|
*LET* statements are mostly used to declare complex computations and to avoid
|
|
repeated computations of the same value at multiple parts of a query.
|
|
|
|
```
|
|
FOR u IN users
|
|
LET numRecommendations = LENGTH(u.recommendations)
|
|
RETURN {
|
|
"user" : u,
|
|
"numRecommendations" : numRecommendations,
|
|
"isPowerUser" : numRecommendations >= 10
|
|
}
|
|
```
|
|
|
|
In the above example, the computation of the number of recommendations is
|
|
factored out using a *LET* statement, thus avoiding computing the value twice in
|
|
the *RETURN* statement.
|
|
|
|
Another use case for *LET* is to declare a complex computation in a subquery,
|
|
making the whole query more readable.
|
|
|
|
```
|
|
FOR u IN users
|
|
LET friends = (
|
|
FOR f IN friends
|
|
FILTER u.id == f.userId
|
|
RETURN f
|
|
)
|
|
LET memberships = (
|
|
FOR m IN memberships
|
|
FILTER u.id == m.userId
|
|
RETURN m
|
|
)
|
|
RETURN {
|
|
"user" : u,
|
|
"friends" : friends,
|
|
"numFriends" : LENGTH(friends),
|
|
"memberShips" : memberships
|
|
}
|
|
```
|
|
|