w10D3 HW for Thursday - Using Sequelize

Question 1

what’s a model file?

Answer 1

a file that’ll be used by the application to query (search/question) the database. (basically like a file that does a fetch to the database)

• it’s used by the express application
• it’s part of the running software

Question 2

what’s a migration file?

Answer 2

a file used to construct the database. It’s like a blueprint for what a table will look like.

• only used by sequelize cli tool to build the database
• it changes your db as your app grows

Question 3

How are migration files different from model files?

Answer 3

Model files can be updated w/o having to remigrate and reseed our database.

Model files are usually used to change one row within a table in some way (ie. creating, reading, updating, deleting), while migrations are meant to build the table in the first place and seed files are meant to just add a bunch of rows at once.

Question 4

How do seeder files interact with migration and model files?

Answer 4

They don’t directly.

Seeder files: keep them in mind when editing migration files.
- when making changes to migration files, be sure to unseed first!

• As long as you seed a table AFTER you migrate it (b/c you can’t add rows to a table that doesn’t exist) it’ll be fine.

Question 5

What are seeder files?

Answer 5

Files where you input data

Question 6

Why do we need a sequelize.close()?

Answer 6

This closes the connection to the database when done with it. we put it at the end of our promise.

ex. 
async function main() {
   ...
   }
   await sequelize.close();
}

main()

Question 7

How do we save a new record with sequelize?

Answer 7

1. we call the static build method on the Cat class (for ex.) with the desired values.
2. we call the save method on the cat instance

Question 8

what does .findByPk(1) do?

Answer 8

The findByPk method obtains only a single entry from the table, using the provided primary key. (in parenthesies)

Pk is primary key. 1 is the id of 1.

Question 9

How do we read a record by primary key?

Answer 9

by using findByPk. be sure to use .close

Question 10

How do we update a record?

Answer 10

.findByPk
update what you want
.save
.close

Be sure to save and close for the update to take effect!

Question 11

How do we destroy a record?

Answer 11

by using .destroy

Question 12

How can you make the create a one step process?

Answer 12

by calling the create class method:

in this example it 1) creates a cat instance and 2) saves the instance method

ex.
const { sequelize, Cat } = require(“./models”);

async function main() {
  const cat = await Cat.create({
    firstName: "Curie",
    specialSkill: "jumping",
    age: 4,
  });

console.log(cat.toJSON());

await sequelize.close();
}

main();

Question 13

What’s the one step method to delete?

Answer 13

use the destroy class method directly:

this example does 1) fetch the record and 2) destroy the instance method

const { sequelize, Cat } = require(“./models”);

async function main() {
  // Destroy the Cat record with id #3.
  await Cat.destroy({ where: { id: 3 } });

await sequelize.close();
}

main();

Question 14

What does JSON.stringify do?

Answer 14

it turns JS into a JSON string

Question 15

What does JSON.parse do?

Answer 15

it turns JSON into JS

Question 16

How do we use sequelize to find just one thing that matches a criteria? Ex. one cat name that matches.

Answer 16

use the .findAll class method

Question 17

How do we use sequelize to find one or another thing that matches a criteria? Ex. one cat name or another

Answer 17

use .findAll class method and where option. the where option tells sequelize to use a WHERE clause.

Question 18

how do you use findAll to find objects that don’t match your criteria?

Answer 18

use the Op object from sequelize.
use [Op.ne]: “Markov” for example to just find names that aren’t equal to “Markov”.

the Op.ne means the “not equal” operator

Question 19

what does ne stand for?

Answer 19

not equal

Question 20

what does Op.or do?

Answer 20

it allows us to find two diff things. here in the ex. below we’re looking to find cats that are either named “Markov” or are age 4

const { Op } = require(“sequelize”);
const { sequelize, Cat } = require(“./models”);

async function main() {
  // fetch cats with name == Markov OR age = 4.
  const cats = await Cat.findAll({
    where: {
      [Op.or]: [
        { firstName: "Markov" },
        { age: 4 },
      ],
    },
  });
  console.log(JSON.stringify(cats, null, 2));

await sequelize.close();
}

main();

Question 21

What does Op.gt and Op.lt do?

Answer 21

it helps us find things that are greater than or less than.

Question 22

What’s Op?

Answer 22

and object is a sequelize operator. it’s used to create more complex comparisons.

https://sequelize.org/v5/manual/querying.html#operators

Question 23

How do we find limiting results with sequelize?

Answer 23

with the limit query option we can limit how many results we want

with findOne we can find one result

Question 24

sequelize validation: how to limit amount of something?

Answer 24

use a len validation with args

[lowNum, highNum]

Question 25

What’s a race condition (transactions)?

Answer 25

the possibility that someone else modifies previously fetched data before you are finished using/updating it.

Question 26

What of the following (whether reading or writing) can take a transaction: tx option?

• findByPk
• findAll
• save
• create
• destory

Answer 26

all of them!

Question 27

What’s the difference between type: sequelize.string/varchar and squelize.text?

Answer 27

string will convert to varchar and they both have more restrictive length (limited amount of text)

text will stay text (unlimited text)

Question 28

what’s the difference between create and build?

Answer 28

create is a 2 in 1 that creates and saves

build requires you to use a save as well in the statement

Question 29

What does the query .allPosts return?

Answer 29

an array of items

Question 30

what does the query .findByPk return?

Answer 30

a single item

Question 31

what does the query .findAll return?

Answer 31

all posts that have a trait that you’re looking for

Question 32

what does the query .findOne return?

Answer 32

a single item

Question 33

For a .findOne query do we need a where clause?

Answer 33

yes!