How do I sum multiple fields in doctrine odm? - php

Question

I want to use doctrine odm's aggregation builder to build this query:
db.TeamStandings.aggregate(
// Pipeline
[
// Stage 1
{
$match: {
"team.$id": ObjectId("5a1643fdf5d8741a883c2aeb")
}
},
// Stage 2
{
$group: {
"_id": { "team": "team.$id" },
// This is the sum of multiple fields
"games": { $sum: { $sum: ["$wins", "$losses", "$ties"] } },
"wins": { $sum: "$wins" },
"losses": { $sum: "$losses" },
"ties": { $sum: "$ties" },
"homeWins" : { $sum: "$homeRecord.wins" },
"homeLosses" : { $sum: "$homeRecord.losses" },
"homeTies" : { $sum: "$homeRecord.ties" },
"roadWins" : { $sum: "$roadRecord.wins" },
"roadLosses" : { $sum: "$roadRecord.losses" },
"roadTies" : { $sum: "$roadRecord.ties" },
}
},
]
);
I executed this in Studio3T and got the following:
{
"_id" : {
"team" : "team.$id"
},
"games" : NumberInt(776),
"wins" : NumberInt(377),
"losses" : NumberInt(398),
"ties" : NumberInt(1),
"homeWins" : NumberInt(218),
"homeLosses" : NumberInt(170),
"homeTies" : NumberInt(1),
"roadWins" : NumberInt(159),
"roadLosses" : NumberInt(228),
"roadTies" : NumberInt(0)
}
How do I write this exact query using doctrine odm's aggregation builder?

Answer 1

This one is tricky because the documentation is not quite clear.
In theory, you create a nested sub-expression and use the sum operator there:
$builder = $this->dm->createAggregationBuilder(\Documents\BlogPost::class);
$builder->group()
->field('id')
->expression(null)
->field('games')
->sum($builder->expr()->sum('$wins', '$losses', '$ties'))
;
However, due to the way the aggregation builder is built, it doesn't quite understand the sum syntax with multiple expressions outside a $project stage, resulting in the following (wrong) result:
[{
"$group": {
"_id": null,
"games": { "$sum": { "$sum": "$wins" } }
}
}]
To work around this problem, use the $add operator instead of $sum in the nested expression:
$builder = $this->dm->createAggregationBuilder(\Documents\BlogPost::class);
$builder->group()
->field('id')
->expression(null)
->field('games')
->sum($builder->expr()->add('$wins', '$losses', '$ties'))
;
This creates the aggregation pipeline you want it to create.
The reason this is weird is because the documentation defines different behavior for $sum when used in $group and $project stages: in $group, it accepts a single argument, while in $project it accepts multiple arguments. However, it is not perfectly clear how it behaves in a nested expression within $group: the fact that the aggregation pipeline you posted works suggests that it doesn't see the sub-expression as being within a $group stage, thus allowing multiple arguments. When I built the operator, I assumed the opposite: only when in a $project stage should $sum accept multiple arguments and default to the one argument syntax otherwise.
I'll create a ticket for this in MongoDB ODM and I'll see if this can easily be fixed.