WEBVTT 1 00:00:01.303 --> 00:00:02.136 In this video, 2 00:00:02.136 --> 00:00:06.136 we'll cover Hibernate one-to one bi-directional. 3 00:00:07.755 --> 00:00:11.036 So, we currently have a uni-directional mapping 4 00:00:11.036 --> 00:00:14.875 between our Instructor and our InstructorDetail 5 00:00:14.875 --> 00:00:16.681 and that's working just fine for us. 6 00:00:16.681 --> 00:00:20.875 We covered all of that in the previous video 7 00:00:20.875 --> 00:00:23.263 but now we have a new use case. 8 00:00:23.263 --> 00:00:27.218 Basically we wanna load an InstructorDetail object 9 00:00:27.218 --> 00:00:30.606 and then we'd like to get the associated Instructor 10 00:00:30.606 --> 00:00:32.859 for that detail object 11 00:00:32.859 --> 00:00:34.750 but we can't really do this 12 00:00:34.750 --> 00:00:38.376 with our current uni-directional relationship, 13 00:00:38.376 --> 00:00:41.327 so right now we can only start with Instructor 14 00:00:41.327 --> 00:00:43.465 and then move to InstructorDetail, 15 00:00:43.465 --> 00:00:45.407 we can't go the other way. 16 00:00:45.407 --> 00:00:49.574 With uni-directional it's really just a one-way street. 17 00:00:50.426 --> 00:00:51.981 But we can actually solve this 18 00:00:51.981 --> 00:00:55.309 by making use of a bi-directional relationship. 19 00:00:55.309 --> 00:00:58.659 So what we can do is start with the InstructorDetail 20 00:00:58.659 --> 00:01:00.866 and then we can actually make it back 21 00:01:00.866 --> 00:01:02.552 to the instructor 22 00:01:02.552 --> 00:01:03.991 and also since we already have 23 00:01:03.991 --> 00:01:06.719 the previous uni-directional relationship in place, 24 00:01:06.719 --> 00:01:08.858 we effectively have bi-directional now, 25 00:01:08.858 --> 00:01:10.978 so now this is a two-way street, 26 00:01:10.978 --> 00:01:12.719 so we can start on any side. 27 00:01:12.719 --> 00:01:14.396 We can start with instructor, 28 00:01:14.396 --> 00:01:15.676 get the InstructorDetail 29 00:01:15.676 --> 00:01:18.438 or start with InstructorDetail 30 00:01:18.438 --> 00:01:21.355 and make it back to the instructor. 31 00:01:22.407 --> 00:01:24.697 So, the nice thing about using bi-directional 32 00:01:24.697 --> 00:01:26.746 is that we have some good news. 33 00:01:26.746 --> 00:01:30.308 We can actually keep our existing database schema 34 00:01:30.308 --> 00:01:34.450 so this is really cool so there's really no changes required 35 00:01:34.450 --> 00:01:35.872 to our database setup, 36 00:01:35.872 --> 00:01:38.012 so we can continue to use the Instructor, 37 00:01:38.012 --> 00:01:39.434 InstructorDetail table 38 00:01:39.434 --> 00:01:41.027 with the foreign keys that we set up 39 00:01:41.027 --> 00:01:43.330 in the previous video. 40 00:01:43.330 --> 00:01:45.855 So, really the only thing that we have to change now 41 00:01:45.855 --> 00:01:48.219 is to simple update the Java code 42 00:01:48.219 --> 00:01:51.552 and we'll cover that part in this video. 43 00:01:54.398 --> 00:01:56.381 Alrighty, so here's our development process, 44 00:01:56.381 --> 00:01:58.908 so we basically need to make some updates 45 00:01:58.908 --> 00:02:01.745 to the InstructorDetail class. 46 00:02:01.745 --> 00:02:05.500 We'll need to add a new field to reference the Instructor 47 00:02:05.500 --> 00:02:07.783 and also add the appropriate getter/setter methods 48 00:02:07.783 --> 00:02:10.493 for Instructor and then we need to add 49 00:02:10.493 --> 00:02:14.523 a OneToOne annotation such that we can point back 50 00:02:14.523 --> 00:02:17.395 to the original Instructor 51 00:02:17.395 --> 00:02:19.964 and then finally, we'll kind of pull it all together 52 00:02:19.964 --> 00:02:21.672 by creating a main application 53 00:02:21.672 --> 00:02:24.255 and we'll test all of this out. 54 00:02:26.369 --> 00:02:28.457 Alrighty, so let's start with step 1.1, 55 00:02:28.457 --> 00:02:32.006 adding a new field to reference Instructor. 56 00:02:32.006 --> 00:02:34.663 So, here's our class here InstructorDetail 57 00:02:34.663 --> 00:02:36.463 and we have the code in place right now 58 00:02:36.463 --> 00:02:38.136 for adding that new field, 59 00:02:38.136 --> 00:02:41.469 so we have a new field named Instructor. 60 00:02:42.349 --> 00:02:45.244 Alright, so step 1.2 add in getter/setter methods 61 00:02:45.244 --> 00:02:47.015 for Instructor, so here we just have 62 00:02:47.015 --> 00:02:48.413 a getter and a setter. 63 00:02:48.413 --> 00:02:50.412 Again, there's no rocket science here. 64 00:02:50.412 --> 00:02:53.389 Basically we can generate this with Eclipse 65 00:02:53.389 --> 00:02:55.828 but the key thing here is that we can call the setter method 66 00:02:55.828 --> 00:02:58.451 for adding an Instructor or setting the instructor, 67 00:02:58.451 --> 00:03:01.156 use the getter method for getting the associated Instructor 68 00:03:01.156 --> 00:03:04.656 with this given InstructorDetail instance. 69 00:03:06.627 --> 00:03:08.355 Now we're moving ahead to step 1.3. 70 00:03:08.355 --> 00:03:11.638 This is where we add the OneToOne annotation. 71 00:03:11.638 --> 00:03:14.610 So, note here on our field for Instructor, 72 00:03:14.610 --> 00:03:16.277 we add the @OneToOne 73 00:03:17.245 --> 00:03:19.328 and then we have a new entry here 74 00:03:19.328 --> 00:03:21.241 that's a little interesting. 75 00:03:21.241 --> 00:03:24.221 We say mappedBy InstructorDetail. 76 00:03:24.221 --> 00:03:27.325 So, what exactly does this refer to 77 00:03:27.325 --> 00:03:28.675 or what does this mean? 78 00:03:28.675 --> 00:03:33.299 Well, this basically refers to the InstructorDetail property 79 00:03:33.299 --> 00:03:35.341 in the Instructor class. 80 00:03:35.341 --> 00:03:36.439 So, what we're telling Hibernate 81 00:03:36.439 --> 00:03:38.483 is that this Instructor field 82 00:03:38.483 --> 00:03:42.548 is actually mapped by the InstructorDetail property 83 00:03:42.548 --> 00:03:45.014 in the Instructor class. 84 00:03:45.014 --> 00:03:47.139 Alright, so that's kind of the mappedBy. 85 00:03:47.139 --> 00:03:51.155 Let's kind of dig into this a little further. 86 00:03:51.155 --> 00:03:52.636 So, a bit more on mappedBy. 87 00:03:52.636 --> 00:03:55.683 So, we have this reference here for mappedBy. 88 00:03:55.683 --> 00:03:58.214 That's in our InstructorDetail class here. 89 00:03:58.214 --> 00:04:00.519 So again, the mappedBy tells Hibernate 90 00:04:00.519 --> 00:04:03.536 to look at the InstructorDetail property 91 00:04:03.536 --> 00:04:05.691 in the Instructor class 92 00:04:05.691 --> 00:04:08.587 so Hibernate can actually use the information 93 00:04:08.587 --> 00:04:11.664 from the Instructor class's join column 94 00:04:11.664 --> 00:04:16.217 to figure out how to find the associated Instructor, 95 00:04:16.217 --> 00:04:18.288 alright, so you're basically telling Hibernate 96 00:04:18.288 --> 00:04:22.932 hey, this field Instructor in InstructorDetail 97 00:04:22.932 --> 00:04:25.276 it's mappedBy InstructorDetail. 98 00:04:25.276 --> 00:04:26.441 Hibernate will go figure that out, 99 00:04:26.441 --> 00:04:28.344 look at the foreign key relationship 100 00:04:28.344 --> 00:04:29.546 and match everything up, 101 00:04:29.546 --> 00:04:32.306 so effectively Hibernate can use this information 102 00:04:32.306 --> 00:04:34.680 to find out how these two items are linked up 103 00:04:34.680 --> 00:04:37.519 and also finding the appropriate Instructor 104 00:04:37.519 --> 00:04:40.186 for this given InstructorDetail. 105 00:04:42.680 --> 00:04:44.018 Alrighty, so that's the mappedBy. 106 00:04:44.018 --> 00:04:46.116 Now, the other thing here is cascading, 107 00:04:46.116 --> 00:04:47.969 so we'll add support for cascading, 108 00:04:47.969 --> 00:04:50.263 so this new entry that I just added here, 109 00:04:50.263 --> 00:04:53.162 cascade equals CascadeType.ALL, 110 00:04:53.162 --> 00:04:55.143 so remember from the previous videos, 111 00:04:55.143 --> 00:04:58.325 this will actually cascade all operations 112 00:04:58.325 --> 00:05:00.339 to the associated Instructor. 113 00:05:00.339 --> 00:05:03.290 So, if I load an InstructorDetail 114 00:05:03.290 --> 00:05:05.839 then if I wanna delete that InstructorDetail, 115 00:05:05.839 --> 00:05:08.131 this will also cascade the delete operation 116 00:05:08.131 --> 00:05:10.197 to that given Instructor 117 00:05:10.197 --> 00:05:12.493 and remember, you have fine grained control 118 00:05:12.493 --> 00:05:14.077 over the cascading types 119 00:05:14.077 --> 00:05:16.065 so if you don't want to cascade all, 120 00:05:16.065 --> 00:05:17.971 you can choose the appropriate cascade types 121 00:05:17.971 --> 00:05:22.282 that you'd like to use for your given use case. 122 00:05:22.282 --> 00:05:23.995 Alright, so we can kind of wrap it up here 123 00:05:23.995 --> 00:05:26.188 and we can wrap it up by creating a main app, 124 00:05:26.188 --> 00:05:27.445 that's our step two. 125 00:05:27.445 --> 00:05:29.090 So, basically what we're gonna do here 126 00:05:29.090 --> 00:05:30.114 is that we're gonna go through 127 00:05:30.114 --> 00:05:33.413 and actually get the InstructorDetail object 128 00:05:33.413 --> 00:05:34.638 from the database, 129 00:05:34.638 --> 00:05:36.685 so I'll set up theId equals one, 130 00:05:36.685 --> 00:05:38.973 that's whatever the ID is 131 00:05:38.973 --> 00:05:41.788 or primary key for that given InstructorDetail object 132 00:05:41.788 --> 00:05:44.261 and then I'll go and grab that InstructorDetail 133 00:05:44.261 --> 00:05:45.115 from the database, 134 00:05:45.115 --> 00:05:48.491 so I do a session.get InstructorDetail.class 135 00:05:48.491 --> 00:05:51.180 and I pass in a reference to theId. 136 00:05:51.180 --> 00:05:52.846 Then what I'll do is kind of move forward here 137 00:05:52.846 --> 00:05:54.249 and I'll print out the details, 138 00:05:54.249 --> 00:05:56.754 so I'll say system.out.print line, 139 00:05:56.754 --> 00:05:58.504 tempInstructorDetail. 140 00:05:59.543 --> 00:06:00.892 And then we'll go through and print out 141 00:06:00.892 --> 00:06:02.007 the associated Instructor. 142 00:06:02.007 --> 00:06:03.764 So, here I'd do a system.out.print line, 143 00:06:03.764 --> 00:06:07.125 and I'll say tempInstructorDetail.getInstructor. 144 00:06:07.125 --> 00:06:10.522 So, remember, now we have this bi-directional relationship, 145 00:06:10.522 --> 00:06:12.697 so by going to the InstructorDetail, 146 00:06:12.697 --> 00:06:15.728 I can get back to the actual Instructor 147 00:06:15.728 --> 00:06:17.597 and print that information out. 148 00:06:17.597 --> 00:06:20.248 So, this is great, so this kind of meets our objectives, 149 00:06:20.248 --> 00:06:22.287 kind of fulfills our requirement 150 00:06:22.287 --> 00:06:24.804 of having this bi-directional relationship 151 00:06:24.804 --> 00:06:28.137 between Instructor and InstructorDetail. 152 00:06:29.345 --> 00:06:31.088 Alrighty, so this is some good information. 153 00:06:31.088 --> 00:06:32.478 What we're gonna do in the next video, 154 00:06:32.478 --> 00:06:34.955 jump into Eclipse and then we'll write this code 155 00:06:34.955 --> 00:06:35.938 and we'll test it out, 156 00:06:35.938 --> 00:06:38.855 so I'll see you in the next video.