Eve: Building RESTful APIs with MongoDB and Flask Transcripts
Chapter: Fine-tuning your REST service
Lecture: Handling datetime values
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One question that often comes up of Stack Overflow is
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how do you store datetime values, and how do you query for them.
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Well, the thing is, Json comes with no date types,
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so usually Rest services fall back to parsing matching strings
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and then store them as datetime values.
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In order for that to work properly however,
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client server need to agree on a standard string format for datetime fields.
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By default, Eve accepts datetime fields as rfc1123 strings,
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this format is the de facto standard in Rest and more in general, on the internet.
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To give you an idea of what an rfc1123 date looks like,
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let's just take a look at the values for the
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updated and created metafields in any Eve document,
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we have a string of course,
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the first value within the string is the actual day, 3 letters,
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comma and then the full date,
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then the hours, minutes and seconds for the time,
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and finally the timezone, very simple, staightforward, easy to read.
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So let's try to perform a query on a date field,
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here for example, I am asking for all the people
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which have been updated at a date greater than or equal to Tue, 20 Feb.
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So let's send this query in and we get a number of documents back, 6 total.
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If we go back and update and change the date to 21 Feb,
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we should get back a couple of documents right, 2 documents total.
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So as you can see, the date we used for our queries
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is matching in format the date we have on the documents,
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and this is the rfc1123 format.
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But what if you need to have
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some different kind of string format in your documents?
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Well, we can do that very easily,
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we just need to go back to our code editor and type in something like this,
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date format is the setting which allows you
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to change the default format for datetime sting values,
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here we are saying to Eve
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I don't want to use rfc1123, I want to use this format instead.
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If you are curious about this string in here,
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you should know that this is the standard Python notation for datetime stings,
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we are using what is called the strf time format
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so you can go here on the Python website and look at the documentation
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where you get a very nice table with all the meanings,
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all the values, strings you can use or directive as they are code
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to the format of your string.
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So back to the editor we go and I am basically saying
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I only want day month and year in my date format.
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Now if I go back to Postman,
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let me first save, and relaunch the server as usual,
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now if we perform the same query here with the old format
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we should get nothing back exactly,
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because there you have no matches for this string format
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but if we say that we only want to use the date with this format here
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which should match the one we defined,
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we should get back on track exactly,
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so two documents and two fields.
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Let's try with 20, 7 documents, yes,
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that makes sense because we are losing precision here
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with the same query we were getting 6 documents before
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but now, we aren't providing any time information,
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so we're getting all the documents for the 20 Feb and one more document.
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Keep in mind that the date format settings
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has an epath not only on the queries, but also on the Json payloads,
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so when you change the format, you also need to change your payloads,
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for example, here I am still trying to write a document
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with the rfc1123 standard format,
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if I try to send a request to my service,
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I get an error because born is not of datetime type,
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it actually is, but it is not conforming to our new standard,
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so what we need to do here, of course, is go and update this field
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and try to post again, and it will work.
