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Creating the PizzaTopping Entity5:50 with Ben Deitch
In this video we'll finish up creating our Entities with the PizzaTopping Entity!
We're almost done creating our entities. 0:00 All we've got left is one combining pizzas with toppings. 0:02 The first step to creating an entity is to create a class. 0:05 To get started, let's create a new pizza topping class inside of our data package. 0:09 And make sure to pick Class. 0:15 Then, just like our other entities, let's make this a data class. 0:18 And declare our columns, a parameters to the constructor. 0:23 So instead of brackets, we want parentheses. 0:28 And inside the parentheses, let's use a val to declare 0:33 pizzaId as the first parameter, and make it an Int. 0:38 Then let's use another val, to declare toppingId 0:43 as the second parameter, and let's make it an Int as well. 0:49 Great, now let's add the @Entity annotation above the class. 0:53 And all that's left is to declare the relationships. 0:59 We'll need to specify the primary key, as well as both foreign keys. 1:03 Let's start with the primary key. 1:07 In the previous video, 1:10 we declared a primary key by using the @primarykey annotation. 1:11 However, this doesn't work if your table has more than one column in its 1:16 primary key. 1:20 For situations like this you have to declare 1:22 the primary key up with the entity. 1:25 Let's add parentheses after the word entity, and 1:27 let me just quickly hide the side pane. 1:30 And then let's look at some of the options we can declare. 1:36 By default, 1:39 each table in the database will be named exactly like its corresponding entity. 1:40 However, if you'd like the table to have a different name, 1:46 you can do that by specifying the table name property. 1:49 In addition to the table name, it looks like there's also entries to let us 1:52 specify multiple primaryKeys, and multiple foreignKeys. 1:56 Let's set up the primaryKeys by typing, 2:02 primaryKeys = arrayOf. 2:09 And inside the array, we just need to add the names of the columns. 2:13 PizzaId. 2:18 And toppingId. 2:22 Also inside annotations, and only inside of annotations, 2:25 we're allowed to declare a raise using brackets. 2:31 Let's use alt+enter on arrayOf to replace this call 2:36 with an array literal, which are the brackets, awesome. 2:41 Now, to add a comma at the end of our array. 2:47 And then add a new line for setting up our foreign keys. 2:51 Let's type foreignKeys=, and remember it needs an array of foreign key objects. 2:55 Let's add the brackets for the array, and then create a new foreign key by typing, 3:01 [(ForeignKey)], and hitting enter to accept auto complete. 3:08 Which for some reason, gives us an extra couple of parentheses. 3:13 Let's get rid of those. 3:18 And then look at which parameters we need to provide. 3:23 We’ll need to specify the first three. 3:30 The entity the foreign key represents, the name of the column and 3:32 the parent table, and the name of the column and this table. 3:36 Referred to as the child columns. 3:40 Also, even though in this case we're only matching one column with one other column, 3:42 it's possible to have a foreign key involving multiple columns. 3:48 So instead of just using a string, 3:51 we'll need to specify each of these columns as an array containing a string. 3:54 Okay, let's start with the pizza foreignKey. 3:59 Its entity is the pizza class. 4:02 So, let's set entity = pizza:: class, 4:04 parentColumns = to an empty array. 4:13 The parent column is just the name of the column that 4:22 the foreign key is referencing. 4:24 Since the pizzaId column corresponds to the id column in the Pizza table, 4:26 that's the one we're looking for. 4:31 Let's add id to our parentColumns array, and then move on to child columns. 4:33 Which is just our pizzaId column. 4:40 So let's add a comma, and then set child columns 4:42 equal to an array containing pizzaId as a string. 4:47 All right, all we've got left is to specify our foreignKey 4:53 to the topping table. 4:57 I'm gonna add a bit of spacing to make it easier to see everything. 4:58 Then let's copy our pizza foreignKey, 5:08 add a comma to the end of the line, and then paste it on the next line. 5:12 Now we've just gotta change pizza to topping, 5:20 and a pizzaId, to toppingId, and there we go. 5:25 The pizza topping table is finished. 5:30 Pretty cool, right? 5:34 We've created a bunch of tables, but we haven't had to right any SQL. 5:35 Thinking back to the last video, once we've created the end of these, 5:39 it's time to create the dows. 5:43 Coming up, we'll take a look at how to query our tables 5:44 by using data access objects. 5:47
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