Let's Review!

[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. 0:07 We used it to get single records out that matched a certain primary key. 0:10 And we used it to get all of the records for 0:14 a certain model like when we made our list of courses. 0:16 We also used it when we were making model formsets and needed a set of blank forms. 0:19 Let's do a mini review. 0:24 We'll use our course model. 0:25 If we want all of the courses that are saved in the database, 0:27 we would use course.objects.all. 0:30 If we didn't want any of them but we wanted a query set, 0:32 we'd use course.objects.none. 0:35 And if we needed just a single course, 0:37 we would use the get method to pull it out using a comparison. 0:40 Of course, if we think that course might not exist, 0:44 we'd use the handy get object or 404 function. 0:47 The last thing we used the ORM for was creating and saving records. 0:51 We used the create method to make a new instance and the save method to save 0:54 changes to an existing one or to insert an in-memory instance into the database. 0:58 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, 1:11 is a collection of records returned from the database. 1:13 You might be expecting the collection to be a set since that's in the name or 1:15 at least unique but that's not always the case. 1:19 Anything that could come back from a plain old SQL query can be in a query set. 1:22 Query sets are also lazy. 1:27 Lazy is a word you'll hear a lot in Django, actually. 1:29 When we use lazy in a programming concept, we usually mean that whatever work 1:32 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. 1:41 They don't hit the database at all until you consume them with Lynn, a slice, 1:43 iteration or some other options. 1:48 I'll include a link to more information about this in the teacher's notes. 1:51 Most of this course will be dealing with the model layer of Django. 1:54 Things like, well, models and query sets. 1:58 So in the next video, let's check out the current state of our models, our data, 2:00 and make a couple of small changes. 2:04