create object chaining using loop

Question

Is there a way to create a chained object from loop? For example input:

["table1","table2","table3"]

output:

  db
  .select(fields)
  .from(table)
  .innerJoin("table1")
  .innerJoin("table2")
  .innerJoin("table3")

another input:

 ["table1","table2","table3","table4","table5"]

output:

  db
  .select(fields)
  .from(table)
  .innerJoin("table1")
  .innerJoin("table2")
  .innerJoin("table3")
  .innerJoin("table4")
  .innerJoin("table5")

Right now i have no idea how to do that except using eval, which isn't something i would like to do.

I need this to join multiple tables using knex, so if there any other way to do so, i will be really happy :)

Answer 1

I think looking into functional programming will help you here.

I used a pipe function from the internet link below but you could use lodash/Ramda/underscore or whatever your fav util library is.

the two main concepts I'm using here is currying and piping.

What is 'Currying'? Currying is when you break down a function that takes multiple arguments into a series of functions that take part of the arguments we are also making use of curring which is returning a function from another function to compose new functions.

https://medium.com/@venomnert/pipe-function-in-javascript-8a22097a538e A pipe function takes an n sequence of operations; in which each operation takes an argument; process it; and gives the processed output as an input for the next operation in the sequence. The result of a pipe function is a function that is a bundled up version of the sequence of operations.

what we're doing here is taking an array, creating a new array of functions we want to apply to a value.

So we want to do a load of joins on a db.

join => con => con.innerJoin(join);

is taking a value i.e "table1" and returning a function that takes a db connection which calls the join and returns for the next one.

const joins = toJoin.map(join => con => con.innerJoin(join)); and this creates are array of functions to pass to pipe.

const db = ({
  select: function (field) {
    console.log('select', field)
    return db
  },
  from: function (table) {
    console.log('from', table)
    return db;
  },
  innerJoin: function (join) {
    console.log('innerJoin', join)
    return db;
  }
});

const _pipe = (a, b) => (arg) => b(a(arg));
const pipe = (args) => [].slice.apply(args).reduce(_pipe);

function joinInnerMultiple(table, fields, toJoin) {
  const joins = toJoin.map(join => con => con.innerJoin(join));

  return pipe(joins)(db.select(fields).from(table)); 
}


joinInnerMultiple("User", "uuid", ["table1", "table2", "table3", "table4", "table5"])