Lodash mapping of nested collections

问题

I have following collection:

var realty = {
  name: 'Realty A',
  entrances: [
    {
      name: 'Entrance A',
      units: [
        {name: 'unitA', contracts: [{contractNo: 'no.963'}, {contractNo: 'no.741'}]},
        {name: 'unitB', contracts: [{contractNo: 'no.789'}, {contractNo: 'no.564'}]}
      ]
    },
    {
      name: 'Entrance B',
      units: [
        {name: 'unitC', contracts: [{contractNo: 'no.419'}, {contractNo: 'no.748'}]},
        {name: 'unitD', contracts: [{contractNo: 'no.951'}, {contractNo: 'no.357'}]}
      ]
    }
  ]
}

And I am trying to extract collection of contracts. I tried using lodash 'map' function as follows: _.map(realty, 'entrances.units.contracts') but 'property' iterate does not work on arrays.

Any idea how can I extract collection of all contracts? Perhaps lodash chain could help but I am not sure how to use it :/.

回答1:

This seems to do the trick

_(realty.entrances).flatMap('units').flatMap('contracts').value()

回答2:

One posibility without lodash

var contractsArray = []

realty.entrances.forEach( e => {
 let units = e.units;
 units.forEach( u => contractsArray.push(u.contracts));
});

回答3:

If you want to get all contracts, using lodash:

_.map(realty.entrances, e => e.units.map(u => u.contracts));

来源：https://stackoverflow.com/questions/49553159/lodash-mapping-of-nested-collections