The upsert block allows performing queries and mutations in a single request. The upsert
block contains one query block and one or more than one mutation blocks. Variables defined
in the query block can be used in the mutation blocks using the uid and val function.
In general, the structure of the upsert block is as follows:
upsert {
query <query block>
[fragment <fragment block>]
mutation <mutation block 1>
[mutation <mutation block 2>]
...
}
Execution of an upsert block also returns the response of the query executed on the state of the database before mutation was executed. To get the latest result, we should commit the mutation and execute another query.
uid Function
The uid function allows extracting UIDs from variables defined in the query block.
There are two possible outcomes based on the results of executing the query block:
- If the variable is empty i.e. no node matched the query, the
uidfunction returns a new UID in case of asetoperation and is thus treated similar to a blank node. On the other hand, fordelete/deloperation, it returns no UID, and thus the operation becomes a no-op and is silently ignored. A blank node gets the same UID across all the mutation blocks. - If the variable stores one or more than one UIDs, the
uidfunction returns all the UIDs stored in the variable. In this case, the operation is performed on all the UIDs returned, one at a time.
val Function
The val function allows extracting values from value variables. Value variables store
a mapping from UIDs to their corresponding values. Hence, val(v) is replaced by the value
stored in the mapping for the UID (Subject) in the N-Quad. If the variable v has no value
for a given UID, the mutation is silently ignored. The val function can be used with the
result of aggregate variables as well, in which case, all the UIDs in the mutation would
be updated with the aggregate value.
Example of uid Function
Consider an example with the following schema:
curl localhost:8080/alter -X POST -d $'
name: string @index(term) .
email: string @index(exact, trigram) @upsert .
age: int @index(int) .' | jq
Now, let’s say we want to create a new user with email and name information.
We also want to make sure that one email has exactly one corresponding user in
the database. To achieve this, we need to first query whether a user exists
in the database with the given email. If a user exists, we use its UID
to update the name information. If the user doesn’t exist, we create
a new user and update the email and name information.
We can do this using the upsert block as follows:
curl -H "Content-Type: application/rdf" -X POST localhost:8080/mutate?commitNow=true -d $'
upsert {
query {
q(func: eq(email, "[email protected]")) {
v as uid
name
}
}
mutation {
set {
uid(v) <name> "first last" .
uid(v) <email> "[email protected]" .
}
}
}' | jq
Result:
{
"data": {
"q": [],
"code": "Success",
"message": "Done",
"uids": {
"uid(v)": "0x1"
}
},
"extensions": {...}
}
The query part of the upsert block stores the UID of the user with the provided email
in the variable v. The mutation part then extracts the UID from variable v, and
stores the name and email information in the database. If the user exists,
the information is updated. If the user doesn’t exist, uid(v) is treated
as a blank node and a new user is created as explained above.
If we run the same mutation again, the data would just be overwritten, and no new uid is
created. Note that the uids map is empty in the result when the mutation is executed
again and the data map (key q) contains the uid that was created in the previous upsert.
{
"data": {
"q": [
{
"uid": "0x1",
"name": "first last"
}
],
"code": "Success",
"message": "Done",
"uids": {}
},
"extensions": {...}
}
We can achieve the same result using json dataset as follows:
curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d '
{
"query": "{ q(func: eq(email, \\"[email protected]\\")) {v as uid\\n name} }",
"set": {
"uid": "uid(v)",
"name": "first last",
"email": "[email protected]"
}
}' | jq
Now, we want to add the age information for the same user having the same email
[email protected]. We can use the upsert block to do the same as follows:
curl -H "Content-Type: application/rdf" -X POST localhost:8080/mutate?commitNow=true -d $'
upsert {
query {
q(func: eq(email, "[email protected]")) {
v as uid
}
}
mutation {
set {
uid(v) <age> "28" .
}
}
}' | jq
Result:
{
"data": {
"q": [
{
"uid": "0x1"
}
],
"code": "Success",
"message": "Done",
"uids": {}
},
"extensions": {...}
}
Here, the query block queries for a user with email as [email protected]. It stores
the uid of the user in variable v. The mutation block then updates the age of the
user by extracting the uid from the variable v using uid function.
We can achieve the same result using json dataset as follows:
curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d $'
{
"query": "{ q(func: eq(email, \\"[email protected]\\")) {v as uid} }",
"set":{
"uid": "uid(v)",
"age": "28"
}
}' | jq
If we want to execute the mutation only when the user exists, we could use Conditional Upsert.
Example of val Function
Let’s say we want to migrate the predicate age to other. We can do this using the
following mutation:
curl -H "Content-Type: application/rdf" -X POST localhost:8080/mutate?commitNow=true -d $'
upsert {
query {
v as var(func: has(age)) {
a as age
}
}
mutation {
# we copy the values from the old predicate
set {
uid(v) <other> val(a) .
}
# and we delete the old predicate
delete {
uid(v) <age> * .
}
}
}' | jq
Result:
{
"data": {
"code": "Success",
"message": "Done",
"uids": {}
},
"extensions": {...}
}
Here, variable a will store a mapping from all the UIDs to their age. The mutation
block then stores the corresponding value of age for each UID in the other predicate
and deletes the age predicate.
We can achieve the same result using json dataset as follows:
curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d $'{
"query": "{ v as var(func: regexp(email, /.*@company1.io$/)) }",
"delete": {
"uid": "uid(v)",
"age": null
},
"set": {
"uid": "uid(v)",
"other": "val(a)"
}
}' | jq
Bulk Delete Example
Let’s say we want to delete all the users of company1 from the database. This can be
achieved in just one query using the upsert block as follows:
curl -H "Content-Type: application/rdf" -X POST localhost:8080/mutate?commitNow=true -d $'
upsert {
query {
v as var(func: regexp(email, /.*@company1.io$/))
}
mutation {
delete {
uid(v) <name> * .
uid(v) <email> * .
uid(v) <age> * .
}
}
}' | jq
We can achieve the same result using json dataset as follows:
curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d '{
"query": "{ v as var(func: regexp(email, /.*@company1.io$/)) }",
"delete": {
"uid": "uid(v)",
"name": null,
"email": null,
"age": null
}
}' | jq
This is a companion discussion topic for the original entry at https://dgraph.io/docs/mutations/upsert-block/