Filling a database with after promises parsing a text file

Question

I'm trying to build a db with bluebird and sqlite3 to manage a lot of "ingredients". So far I've managed to parse a file and extrapolate some data from it using regex.

Every time a line matches the regex I want to search in the database if an element with the same name has already been inserted, if so the element is skipped, otherwise it must be inserted. The problem is that some elements get inserted more than one time. The code partially works, and I'm saying it partially works because if I remove the line of code where I check the existence of an element with the same name, the duplicate rows are much more.

Here's the piece of code:

 lineReader.eachLine(FILE_NAME, (line, last, cb) => {
      let match = regex.exec(line);
      if (match != null) {
          let matchedName = match[1].trim();

          //This function return a Promise for all the rows with corresponding name
          ingredientsRepo.getByName(matchedName)
             .then((entries) => {
                 if (entries.length > 0) {
                     console.log("ALREADY INSERTED INGREDIENT: " + matchedName)
                 } else {
                     console.log("ADDING " + matchedName)
                     ingredientsRepo.create(matchedName)
                 }
          })   
      }
 });

I know I'm missing something about Promises but I can't understand what I'm doing wrong.

Here's the code of Both getByName(name) and create(name):

create(name) {
    return this.dao.run(
        `INSERT INTO ingredients (name) VALUES (?)`,
        [name]
    )
}


getByName(name) {
    return this.dao.all(
        'SELECT * FROM ingredients WHERE name == ?',
        [name]
    )
}

Answer 1

ingredientsRepo.getByName(matchedName) returns a promise, this means it's asynchronous. I am also guessing that ingredientsRepo.create(matchedName) is asynchronous, because you are inserting something into a DB.

Your loop doesn't wait for these async functions to complete. Hence the loop could already be on the 50th iteration, when the .then(...) is called for the first iteration.

So let's say the first 10 elements have the same name. Well, since the asynchronous functions take some time to complete, the name will not be inserted into the DB until say maybe the 20th iteration of the loop. So for the first 10 elements, the name does not exist within the DB.

It's a timing issue.