CODEWITHSUNDEEP
javascriptpromisebluebirdknex.js
Rob Wilkerson
Rob Wilkerson

Reputation: 41236

Why is my promise chain failing?

I'm trying to seed a database using knex. With the help of a contributor, I've successfully seeded one table where I need to take several steps:

  1. I need to pull id values from a couple of external tables so I can populate the seeding table's foreign key values.
  2. Generate n records in the seeding table.
  3. Populate the table.

As mentioned, I have this working for one table. Because I'm smarter than a roofing tack and have to do almost the exact same thing for another table, I just copied what was working in the first seed file, dropped it into the second seed file, made a couple of appropriate modifications (specifically, in the second table I only have to populate 1 foreign key value at this point) and...it doesn't work.

I'm at a loss. Surely there's some stupid little thing I'm missing in this code, but I can't find it. I'm trying to seed a units table that I have to populate with a properties.id value.

exports.seed = function(knex, Promise) {
    console.log('Seeding the %s table...', tableName);

    Promise.resolve([
        'properties',
    ])
    .map(function(table) {
        // Pull foreign key values (property_id)
        var ids = knex.select('id').from(table).pluck('id');

        // AT THIS POINT THE ids VARIABLE HAS A VALUE

        return ids;
    })
    .spread(function(properties) {
        // BUT I NEVER SEE THIS LOG PRINT
        console.log('SPREADING UNITS');
    });
};

What am I doing wrong? I've dropped .catch() and .error() into this thing, but nothing gets written to the log. Somehow I just never seem to drop into the .spread(...) method.

UPDATE

For whatever it's worth, this is the content of the .map method before it's returned...

{ client:
   { Formatter: { [Function: Formatter_MySQL] super_: [Function: Formatter] },
     Raw: { [Function: Raw_MySQL] super_: [Object] },
     Transaction: { [Function: Transaction_MySQL] super_: [Object] },
     QueryBuilder: { [Function: QueryBuilder_MySQL] super_: [Object] },
     QueryCompiler: { [Function: QueryCompiler_MySQL] super_: [Function: QueryCompiler] },
     migrationConfig: { tableName: 'knex_migration', directory: './migrations' },
     seedConfig: { directory: './seeds' },
     Runner: { [Function: Runner_MySQL] super_: [Function: Runner] },
     connectionSettings:
      { host: '127.0.0.1',
        port: '3306',
        user: 'root',
        password: '',
        database: 'realster',
        timezone: 'UTC',
        charset: 'utf8',
        debug: false },
     Pool: { [Function: Pool_MySQL] super_: [Function: Pool] },
     databaseName: 'realster',
     pool: { client: [Circular], config: [Object], genericPool: [Object] },
     _events: { start: [Function], query: [Function] },
     Seeder: { [Function: Seeder_MySQL] super_: [Function: Seeder] } },
  _single: { table: 'properties', pluck: 'id' },
  _statements:
   [ { grouping: 'columns', value: [Object] },
     { grouping: 'columns', type: 'pluck', value: 'id' } ],
  _errors: [],
  _joinFlag: 'inner',
  _boolFlag: 'and',
  _notFlag: false,
  and: [Circular],
  _method: 'pluck' }

Upvotes: 4

Views: 504

Answers (1)

Guilherme Rodrigues
Guilherme Rodrigues

Reputation: 2854

You are using spread, which is a method of Promise, in the result of a map.

The map probably produces an array, which doesn't have a spread() function.

Also, spread usually receives a callback with multiple arguments. If you need an array, simply use good old then.

In summary, I guess your code should look more like this:

var mapProperties = function(table) {
  return knex.select('id').from(table).pluck('id');
};

Promise.resolve([
  'properties'
])
.then(mapProperties)
.then(function(properties) {
  console.log(properties);
});

Upvotes: 1

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