基于Lodash提取嵌套集合中合同数据的技术问询

Hey there! Extracting those nested contracts from your realty structure with Lodash is totally straightforward. Here are a few practical, clean approaches to get all contract objects into a single array:

Approach 1: Chained flatMap Calls #

This method is explicit and easy to follow, breaking down the nested extraction step by step:

const _ = require('lodash');

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'}]} ] } 
  ] 
};

const contracts = _.chain(realty.entrances)
  .flatMap('units') // Pull all units from every entrance, flatten into one array
  .flatMap('contracts') // Pull all contracts from every unit, flatten into the final array
  .value();

• _.chain() enables Lodash method chaining for cleaner, more readable code
• flatMap('units') iterates over each entrance, extracts its units array, and flattens the result
• flatMap('contracts') repeats the process for units to collect all nested contracts

Approach 2: flatMapDeep for Recursive Flattening #

If you anticipate deeper nesting in the future, flatMapDeep handles recursive flattening automatically:

const contracts = _.flatMapDeep(realty.entrances, entrance => 
  entrance.units.map(unit => unit.contracts)
);

Or a more concise one-liner:

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

This method recursively flattens all layers of nested arrays, making it flexible for evolving data structures.

Approach 3: Nested flatMap Calls (No Chaining) #

If you prefer avoiding method chaining, you can nest flatMap calls directly:

const contracts = _.flatMap(_.flatMap(realty.entrances, 'units'), 'contracts');

This achieves the exact same result as the chained approach, just in a more compact, non-chained format.

Expected Output #

All three methods will return this array of contract objects:

[
  { contractNo: 'no.963' },
  { contractNo: 'no.741' },
  { contractNo: 'no.789' },
  { contractNo: 'no.564' },
  { contractNo: 'no.419' },
  { contractNo: 'no.748' },
  { contractNo: 'no.951' },
  { contractNo: 'no.357' }
]

内容的提问来源于stack exchange，提问作者Jan Tajovsky