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Data Persistence with Room

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Choosing Queries

1:47 with Ben Deitch

In this video we'll take a look at which queries we'll need to represent in our Data Access Objects!

We've created all of our entities, which represent the tables in our database. 0:00
Now it's time to create the data access objects, or 0:05
DAOs, which represent the queries we need for each of those tables. 0:08
But before we start creating anything, let's talk about what queries we need, and 0:12
which table those queries belong to. 0:16
In main activity, we display a list of all the pizzas. 0:20
To generate this list, 0:24
we'll need a query to select all the pizzas from the pizza table. 0:25
Once we select a pizza, we take that pizza's ID and 0:29
pass it into the creator activity. 0:32
Here, in order to display the pizza, we'll need to retrieve its name, 0:35
as well as which toppings are associated with that pizza. 0:38
To get the name, we'll use a query to return a pizza by its id, and 0:42
then just access the name property. 0:46
But to get which toppings are on a pizza, we'll actually need two queries. 0:49
[SOUND] One to get which topping ids belong with our pizza id, and 0:53
then another to get which toppings belong with those topping ids. 0:57
To populate the Recycler view at the bottom, 1:01
we'll also need a query to retrieve all the toppings. 1:03
Once a user has created their pizza, they'll probably want to save it. 1:06
To handle saving a pizza, we'll need two insert statements. 1:10
One for saving its data to the pizza table, and one for 1:14
saving its toppings to the pizza topping table. 1:16
Likewise, to let users delete a pizza, we'll need queries to remove a pizza from 1:20
both the pizza table, as well as the pizza topping table. 1:24
Last but not least, to let us populate our topping table, 1:27
we'll need an insert statement. 1:31
It may seem like a lot of queries, but 1:33
broken out into which queries along with which table, it's really not so bad. 1:35
Awesome, now that we know which queries we need to create, 1:41
let's start creating them in the next video. 1:44