用sequelize链接查询

Question

In sequelize I want to do something like chaining findAll function calls.

I would like to make a findAll on a model like

const newYorkers = await People.findAll({ where: { city: 'New York' } });

and then use newYorkers as parameter for a function, that makes another findAll on that

const get5ThAvenueInhabitants = (citiesInhabitants) => {
  return await citiesInhabitants.findAll({ where: { street: '5th Avenue' } });
};

get5ThAvenueInhabitants(newYorkers);

That won't work, because after the first findAll, the result isn't a model anymore, but an array of results.

Is it possible to achieve this with sequelize?

Answer 1

If all you want to do is findAll People who live in New York and 5th Avenue , why don't you use and operator?

It would be as simple as

const newYorkers = People.findAll({ 
  where: { 
       city: 'New York',
       street: '5th Avenue',
      },
    ],
  },
});

Answer 2

First besides what you asking, I don't understand the logic behind the function get5ThAvenueInhabitants() . As the previous answer, you can filter directly using where: { city: 'New York', street: '5th Avenue'} . There is no need to query first 'New York' and then '5th Avenue'.

Now coming back on what you really ask, about chaining the request you can use async/await like this:

const mainFunction = async () => {
    const newYorkers = await People.findAll({ where: { city: 'New York' } });
    get5ThAvenueInhabitants(newYorkers);
}

This way, the newYorkers will wait untill all the data is fetch and then proceed to get5ThAvenueInhabitants() .

Answer 3

As you mention, People.findAll({ where: { city: 'New York' } }); returns an array of instances and not a model . The instance object does expose methods like destroy , update , etc., and so you can, in a sense, do a kind of query "chaining", by using the methods on a returned instance, like this:

People.findAll({ where: { city: 'New York' } }).then(people => {
     people.forEach(person => {
         person.destroy();
     })
 });

To filter the returned collection in your application code, as opposed to using a DB query, you could do something like this:

 People.findAll({ where: { city: 'New York' } }).then(people => {
     people.filter(person => {
        if(person.street === '5th Avenue'){
            return person;
        }
     })
 });