Support field functions

[JimmyCheng]

In SQL language, we can apply simple functions to the fields, including create new fields.
e.g.

SELECT concat(first_name, ' ' , last_name) AS full_name
SELECT A, B, 'c' as C from MyTable
SELECT ROUND(Weight_kg / (Height_m * Height_m), 2) AS BMI from ...

In DGraphQL, is it possible to support following kind of query?

{
 allNodes(func: eq(type, "DP")){
     supplyDate
     consumeDate
     status
     issueBehindSchedule: math(supply_date > consume_date)
     noSupplyDate: eq(supplyDate, null)
     atRisk: eq(status, "At Risk")
  }
}

[pawanrawal]

atRisk: eq(status, "At Risk")

I am assuming that here you want all nodes with type DP but want the status value to be returned only if it equals At Risk?

[JimmyCheng]

Here the fields "issueBehindSchedule", "noSupplyDate", "atRisk" are calculated fields according to the existing fields. the value here are "true" or "false". There are some other requirements like simple inline string, date functions.

[manishrjain]

It sounds like an interesting feature, but not sure how useful it is. All of these can be done at the application layer, without necessarily needing the DB to make these calculations.

[campoy]

Hi there,

I just wanted to inform you that at least one part of your request is already doable with the current state of GraphQL+-.

Predicates are not allowed in mathematical expressions, only variables are, so you will need to do the following in order to get a issueBehindSchedule field:

{
 allNodes(func: eq(type, "DP")){
     sd as supply_date
     cd as consume_date
     issueBehindSchedule: math(sd > cd)
  }
}

The rest of your comparisons will still not work since we do not support string comparison yet.

I am considering new features for Dgraph 1.2 (coming up ~ end of Q3) and would love to know more about your constraints to figure out what solution would be best.
I also would like to make sure you understand I'm not guaranteeing this will be implemented, as GraphQL and other features have higher priority.

Please let me know if you'd be interested on a quick chat.