how to populate sub docs mongoose code example

Example 1: populate subdocument mongoose

ProjectMetadata.findOne({id:req.params.prjId})
    .populate(
        [{
        path:'tasks',
        model:TaskMetadata,
        populate:[{
            path:'assigned_to',
            model:User,
            select:'name employee_id'
        },
        {
            path:'priority',
            model:Priority,
            select:'id title'
        }],
        select:"task_name id code assign_to stage priority_id"
    },
    {
        path:'client',
        model:Client,
        select:"client_name"
    },
    {
        path:'prjct_mgr',
        model:User,
        select:"name"
    },
    {
        path:'acc_exec',
        model:User,
        select:'name employee_id'
    },
    {
        path:'poc',
        model:User,
        select:'name employee_id'
    },
    {
        path:'prj_type',
        model:ProjectType,
        select:"type -_id"
    }

])

Example 2: how to use mongoose populate

function getUserWithPosts(username){  return User.findOne({ username: username })    .populate('posts').exec((err, posts) => {      console.log("Populated User " + posts);    })}