planka/server/api/controllers/project-memberships/create.js

const Errors = {
  PROJECT_NOT_FOUND: {
    notFound: 'Project is not found'
  },
  USER_NOT_FOUND: {
    notFound: 'User is not found'
  },
  PROJECT_MEMBERSHIP_EXIST: {
    conflict: 'Project membership is already exist'
  }
};

module.exports = {
  inputs: {
    projectId: {
      type: 'number',
      required: true
    },
    userId: {
      type: 'number',
      required: true
    }
  },

  exits: {
    notFound: {
      responseType: 'notFound'
    },
    conflict: {
      responseType: 'conflict'
    }
  },

  fn: async function(inputs, exits) {
    const project = await Project.findOne(inputs.projectId);

    if (!project) {
      throw Errors.PROJECT_NOT_FOUND;
    }

    const user = await sails.helpers.getUser(inputs.userId);

    if (!user) {
      throw Error.USER_NOT_FOUND;
    }

    const projectMembership = await sails.helpers
      .createProjectMembership(project, user, this.req)
      .intercept('conflict', () => Errors.PROJECT_MEMBERSHIP_EXIST);

    return exits.success({
      item: projectMembership,
      included: {
        users: [user]
      }
    });
  }
};