Example of entity relations in a Cloudant design document.

relations.js

{
  // name of the design doc
  _id: '_design/relations',
  views: {
    lib: couchapp.loadFiles(__dirname + '/../lib'),
    // collate entity relations using 
    collate: {
      map: function (doc) {
        var deref = require('views/lib/index').deref,
            relation = deref[doc.type];
        if (relation) {
          for (var key in relation) {
            emit([doc[key], relation[key], key], null);
          }
        }
        emit([doc._id, doc.type], null);
      },
      reduce: '_count'
    }
  },
  lists: {
    // indicates what items belong to which -- like a reverse JOIN
    belongs: function (head, req) {
      var results = {},
          row;
      try {
        while (row = getRow()) {
          var id = row.key[0];
          if (id === row.id) {
            results[id] = row.doc || row;
          } else {
            var rel = row.key[2];
                // field = row.key[2];
            if (!results[id]) {
              results[id] = {};
            }
            if (!results[id][rel]) {
              results[id][rel] = [];  
            }
            results[id][rel].push(row.doc || row);
          }
        }

        send(JSON.stringify(results)); 
      } catch (e) {
        if (e.message === "row.key is null") {
          send('Request must not reduce results; disable reduce with `reduce=false` in the querystring.');
        } else {
          send(JSON.stringify(e));
        }
      }
    },
    // object dereferencing; a JOIN equivalent
    owns: function (head, req) {
      var deref = require('views/lib/index').deref,
          results = {},
          rows = [],
          row;
      try {
        while (row = getRow()) {
          rows.push(row);
        }
        
        rows.forEach(function (row) {
          if (row.key.length === 2) {
            results[row.id] = row.doc || row;
          }
        });

        rows.forEach(function (row) {
          if (row.key.length === 3) {
            var target = row.key[0],
                field = row.key[2];

            results[row.id][field] = results[target];
          }
        });

        send(JSON.stringify(results));
      } catch (e) {
        if (e.message === "row.key is null") {
          send('Request must not reduce results; disable reduce with `reduce=false` in the querystring.');
        } else if (e.message === "results[row.id] is undefined") {
          send('Request must contain all rows; don\'t use `key`, `keys`, `startkey`, and `endkey` as options for this list function.');
        } else {
          send(JSON.stringify(e));
        }
      }
    }
  },
  shows: {
    // show code goes here
  }
};