title: How create relationship between two collections
body: <p>I'm creating server app using nodejs(express) and mongodb(mongoose). I must create relationships between Organization model and Users model. After creating an organization, I want to create a user that will apply to a specific organization. One user can apply to many organizations. How can I do this?</p>
  
  <pre><code>const mongoose = require("mongoose");
  const Schema = mongoose.Schema;
  // UserShema
      const UserSchema = Schema({
        login: {
          type: String,
          require: true,
          unique: true
        },
        password: {
          type: String,
          require: true
        },
        organization: {
          ref: "Organization",
          type: Schema.Types.ObjectId
        }
      });
  
      // Organization Schema
      const OrganizationSchema = Schema({
        label: {
          type: String
        },
        users: [{
          type: Schema.Types.ObjectId,
          ref: "Users"
        }]
      });
  
      //For now I have simple route for creating an Organization.
      // request: 
      //  {
      //    "label": "testOrg"
      //  }
  
      exports.createOrganization = async (req, res) =&gt; {
        try {
          const org = await new Organization(req.body);
          await org.save();
        } catch (error) {
          return res.status(500).json({error})
        }
      }
  
      //And I have this route for user registration
  
      exports.signup = async (req, res) =&gt; {
        const errors = validationResult(req);
        if (!errors.isEmpty()) {
          return res.status(400).json({ errors: errors.array() });
        };
        const {login} = req.body;
        try {
          const checkUser = await Users.findOne({login});
          if (!checkUser) {
            const user = await new Users(req.body);
            await user.save();
            return res.status(200).json({ user });
          } else {
            return res.status(400).json({error: "User already exist"})
          }
        } catch (error) {
          return res.status(500).json({error})
        }
      };
  </code></pre>