Stage 2 · Lesson 4 of 9
Projection: choosing the fields you get back
The second argument to find is a , which chooses the returned. { title: 1, year: 1 } returns only those fields plus _id, and { plot: 0 } returns everything except plot. You cannot mix including and excluding in one projection, except that you may exclude _id in an inclusion projection with _id: 0.
works for nested fields, and $slice returns part of an . Projection matters more than it looks. Documents can be large, and returning only what a page needs saves network, memory and time, and it makes covered queries possible in the indexing stage.
Common trapfetching whole documents everywhere because it is easier, then wondering why a list page moves megabytes of data it never shows.
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Resources for this stage
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- CourseFreeMongoDB University
MongoDB
Free: the CRUD lessons on inserting, finding, replacing, updating and deleting documents, with labs