Eve: Building RESTful APIs with MongoDB and Flask Transcripts
Chapter: Fine-tuning your REST service
Lecture: Client and server projections
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Projections are a powerful feature,
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they allow a client to dictate of all document fields
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which ones should be returned with the response.
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In this request here we're asking for just the last name field
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let's send it over and we can see that all the documents still have
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the meta fields because these are always included
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no matter the projection. We can also exclude fields,
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for example, here I'm excluding the last name field
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I want all the fields but not last name
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and as you can see, here we're getting first name, location,
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age, role, etc, but no last name.
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Projections are nice because they allow the client
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to pick only the fields it really needs.
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Imagine if the people document had a picture
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if we don't need a picture, we can just exclude it
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and we won't be forced to download it, how nice is that?
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You can, of course, disable projections
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you simply go to the code editor in your settings file
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and set projection to false.
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This is global, and as you might expect by now
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you can go and switch it on at local level if you want to.
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So now projections are disabled at all endpoints but people.
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Of course, we can also change the word used to query for a projection
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let me save, relaunch, go back to Postman,
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and use fields instead. Got it.
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Now, so far we've have seen that the client can control projections
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but we can actually predefine projections on server side.
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Let's see how we do that.
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Let's first clean up a little bit,
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all right, we define server side projections at the endpoint level,
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let me paste an example here,
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data source is dictionary and it allows the projection key
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do not confuse this projection key with root level projection boolean
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which allows you to turn projection feature on and off.
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So here we're setting a projection server side
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every request sent to the people endpoint
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will not include last name by default
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let's try this, save, relaunch as usual and let's ask for people
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without any client projection, same response.
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No last name included with the response
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as you can see, clients can still alter the output if they wish
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but that the default is a different projection
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it is a server projection,
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default server side projection can come in handy in several situations
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one is the picture we mentioned before,
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you aren't letting the clients download it by default
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but they can still go and require it with a specific projection should they need it.
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Also keep in mind that projections are a read-only thing
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they don't apply to write operation.
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You still have a schema endpoint and clients can still write
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the world document or edit the world document as they please.
