CODEWITHSUNDEEP
mongodb
Rakesh Prasad
Rakesh Prasad

Reputation: 642

how to add static column to mongo select statement

I want to write a mongo statement which is equivalent to this SQL statement. I know how to grab all the columns from table, but not sure how to get a column with static value out. Here is query:

select a.* , "static_value1" from table_a a;

Upvotes: 2

Views: 601

Answers (1)

Mark
Mark

Reputation: 6404

Give a try to the following one by using aggregate and literal:

Let's say we have the following input:

db.inventory.insertMany( [
  { item: "journal", status: "A", size: { h: 14, w: 21, uom: "cm" }, instock: [ { warehouse: "A", qty: 5 } ] },
  { item: "notebook", status: "A",  size: { h: 8.5, w: 11, uom: "in" }, instock: [ { warehouse: "C", qty: 5 } ] },
  { item: "paper", status: "D", size: { h: 8.5, w: 11, uom: "in" }, instock: [ { warehouse: "A", qty: 60 } ] },
  { item: "planner", status: "D", size: { h: 22.85, w: 30, uom: "cm" }, instock: [ { warehouse: "A", qty: 40 } ] },
  { item: "postcard", status: "A", size: { h: 10, w: 15.25, uom: "cm" }, instock: [ { warehouse: "B", qty: 15 }, { warehouse: "C", qty: 35 } ] }
]);

Calculated field:

And I want as a custom result something like this:

{ "_id" : ObjectId("5c6b7e7449a55d3136613f90"), "myCustomField" : true }

To achieve the custom field, which is myCustomField in this example:

db.inventory.aggregate([ { $project: { myCustomField: { $eq: ["$status", { $literal: "A" }] }} }]);

Custom static value field

If you do not want to have calculated fields, simply use the following expression:

db.inventory.aggregate([ { $project: { myCustomField: { $literal: "apple" } } }]);

Which results as:

{ "_id" : ObjectId("5c6b7e7449a55d3136613f8c"), "myCustomField" : "apple" }

Doc: $literal

Upvotes: 2

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