Use $project to display data in a specific order

Use $project to display data in a specific order

Situation: In an Aggregation pipeline, you may want to display data being $project-ed in a specific order.

Here’s how you’d do it. Put an underscore to the key names _variable and reference the actual variable in the value, _variable: "$variable". See this stack overflow for reference.

# pay attention to first $project
db.bounties.aggregate([
    {$match: {"$and": [{season: 2}, {customer_id: '905250069463326740'}]}},
    {$project: {_id: 0, _customer_id: "$customer_id", _title: "$title", _status: "$status", _createdAt: "$createdAt", _claimedAt: "$claimedAt", _submittedAt: "$submittedAt", _reviewedAt: "$reviewedAt"}},
    {$project: {_id: 0, customer_id: "$_customer_id", title: "$_title", status: "$_status", createdAt: "$_createdAt", claimedAt: "$_claimedAt", submittedAt: "$_submittedAt", reviewedAt: "$_reviewedAt"}}
])

Use $project twice to get original field names

Situation: After displaying in a specific order, you may want to retain the original field name. To do this, you’d use $project again.

# pay attention to second $project
db.bounties.aggregate([
    {$match: {"$and": [{season: 2}, {customer_id: '905250069463326740'}]}},
    {$project: {_id: 0, _customer_id: "$customer_id", _title: "$title", _status: "$status", _createdAt: "$createdAt", _claimedAt: "$claimedAt", _submittedAt: "$submittedAt", _reviewedAt: "$reviewedAt"}},
    {$project: {_id: 0, customer_id: "$_customer_id", title: "$_title", status: "$_status", createdAt: "$_createdAt", claimedAt: "$_claimedAt", submittedAt: "$_submittedAt", reviewedAt: "$_reviewedAt"}}
])

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