MongoDB script that returns a flattened list of all fields ever used on a specific collection

dbFields.js

// Return a flattened list of all fields ever used on a MongoDB collection.
// Usage: `mongo --quiet <database> dbFields.js`

// Collection for which to get fields
var collection = 'users';

// Determines how to represent the keys of an array of objects.
// This allows for differentiating between nested objects and nested arrays of objects.
//
// e.g. for a document
// { education: [
//   {university: 'umich', city: 'Ann Arbor'},
//   {university: 'mit', city: 'Cambridge'}
// ]}
//
// using an array separator of "$" would represent the flattened keys as "education.$.university", "education.$.city"
var arraySeparator = '$'; // Set to '' to omit

// Flattens documents fields into "dot-notation" for nested attributes
var flatten = function(obj, into, prefix) {
  into = into || {};
  prefix = prefix || '';
  for (var k in obj) {
    if (obj.hasOwnProperty(k)) {
      var prop = obj[k];
      if (prop && typeof prop === 'object' && !(prop instanceof Date || prop instanceof RegExp)) {
        if (!isNaN(Number(k))) {
          // Collapse arrays into a single object
          flatten(prop, into, prefix + (arraySeparator.length ? arraySeparator + '.' : ''));
        } else {
          flatten(prop, into, prefix + k + '.');
        }
      } else {
        if (k === 'str') {
          // Flatten _id reference fields
          into[prefix.slice(0, -1)] = prop;
        } else if (isNaN(Number(k))) {
          // Skip arrays of values
          into[prefix + k] = prop;
        }
      }
    }
  }
  return Object.keys(into);
};

// Return unique values for an array
var unique = function(array) {
  var results = [];
  var seen = [];
  array.forEach(function(value, index) {
    if (seen.indexOf(value) === -1) {
      seen.push(value);
      results.push(array[index]);
    }
  });
  return results;
};

var fields = []

// Concatenate flattened fields for all objects into a single array
db[collection].find().forEach(function(doc) {
  fields = unique(fields.concat(flatten(doc)));
});

print(fields);

dbFirstLevelFields.js

// Similar to `dbFields.js`, but without recursive nesting.
// It only looks at the first level of an Array or Object.

var collection = 'conversations';
var arraySeparator = '$';

var isArray = function(obj) {
  return Object.prototype.toString.call(obj) === '[object Array]';
};

var isObject = function(obj) {
  return typeof obj === 'object' && !!obj && !(obj instanceof Date);
};

var unique = function(array) {
  var results = []; 
  var seen = []; 
  array.forEach(function(value, index) {
    if (seen.indexOf(value) === -1) {
      seen.push(value);
      results.push(array[index]);
    }   
  }); 
  return results;
};

var getKeys = function(obj, parent, array) {
  var keys = []; 
  Object.keys(obj).forEach(function(key) {
    if (parent) {
      if (array) {
        keys.push(parent + '.' + arraySeparator + '.' + key);
      } else {
        keys.push(parent + '.' + key);
      }   
    } else {
      keys.push(key);
    }
  });
  return keys;
};

var getFields = function(doc) {
  var fields = [];
  getKeys(doc).forEach(function(key) {
    fields.push(key);
    if (isArray(doc[key])) {
      doc[key].forEach(function(subDoc, i) {
        if (isObject(doc[key][i])) {
          fields = fields.concat(getKeys(subDoc, key, true));
        }
      });
    } else if (isObject(doc[key]) && key.substr(0, 1) !== '_') {
      fields = fields.concat(getKeys(doc[key], key));
    }
  });
  return fields;
};

var fields = [];
db[collection].find().forEach(function(doc) {
  fields = unique(fields.concat(getFields(doc)));
});

print(fields);