1-8 查询

user表
{
  name:"chengchao",
  cartLists:[
    {name:"html",like:true},
    {name:"css",like:false},
     {name:"js",like:false}
  ]
}

1 只查询cartLists这个内嵌数组

db.user.find({},{history:1})
db.user.aggregate([{$project:{history:1}}])