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What's the ORM used for again? And what methods have we used? If you have these questions in mind, we can answer them!
[MUSIC]
0:00
Hi, I'm Kenneth,
the Python teacher here at Treehouse.
0:04
We've been using Django's ORM in
all of our agenda courses so far.
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We used it to get single records out
that matched a certain primary key.
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And we used it to get
all of the records for
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a certain model like when we
made our list of courses.
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We also used it when we were making model
formsets and needed a set of blank forms.
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Let's do a mini review.
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We'll use our course model.
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If we want all of the courses
that are saved in the database,
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we would use course.objects.all.
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If we didn't want any of them but
we wanted a query set,
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we'd use course.objects.none.
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And if we needed just a single course,
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we would use the get method to
pull it out using a comparison.
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Of course,
if we think that course might not exist,
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we'd use the handy get object or
404 function.
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The last thing we used the ORM for
was creating and saving records.
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We used the create method to make a new
instance and the save method to save
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changes to an existing one or to insert
an in-memory instance into the database.
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But even with all of that,
1:03
there's still a lot about the ORM
that we haven't looked at.
1:04
I mean, heck, I haven't even given you a
formal definition for what a query set is.
1:07
A query set, at least in Django's terms,
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is a collection of records
returned from the database.
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You might be expecting the collection
to be a set since that's in the name or
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at least unique but
that's not always the case.
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Anything that could come back from a plain
old SQL query can be in a query set.
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Query sets are also lazy.
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Lazy is a word you'll hear
a lot in Django, actually.
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When we use lazy in a programming concept,
we usually mean that whatever work
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the lazy thing is going to do won't
be done until we use the lazy thing.
1:36
For instance,
query sets exist only in memory.
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They don't hit the database at all until
you consume them with Lynn, a slice,
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iteration or some other options.
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I'll include a link to more information
about this in the teacher's notes.
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Most of this course will be dealing
with the model layer of Django.
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Things like, well, models and query sets.
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So in the next video, let's check out
the current state of our models, our data,
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and make a couple of small changes.
2:04
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