// 2024_4_17.js

// Mongosh
mongosh.exe

// Set up toyu DB in Mongo.
mongorestore --archive="toyu-db.gz" --gzip --nsFrom='toyu.*' --nsTo='toyu.*'

// [1] Show all students.
use toyu

db.student.find()

// db.collection.find(query, projection, options)

// Getting rid of _id:
// query: {}
// projection: { "_id": 0 } 
db.student.find({},
   { "_id": 0 }  
)

db.student.find({},
   { "_id": false }  
)

students = db.student.find({},
   { "_id": false }  
)

// Show all information of students majoring in 'CINF'.
// query: {"major": "CINF"}
db.student.find({"major": "CINF"},
    { "_id": 0 }
)

// Show all student names. Return an array of student objects.
db.student.find({},
   { "fname": 1, "lname":1, "_id": 0 }  
)

db.student.find({"major": "CINF"},
   { "fname": 1, "lname":1, "major": 1, "minor": 1, "_id": 0 }  
)

[4] Show all student names in this format:
student #0: Tony Hawk
student #1: Mary Hawk
student #2: David Hawk
student #3: Catherine Lim
student #4: Larry Johnson
student #5: Linda Johnson
student #6: Lillian Johnson
student #7: Ben Zico
student #8: Bill Ching
student #9: Linda King
Solution:
result = db.student.find({},
   { "fname": 1, "lname":1, "_id": 0 }  
).toArray()

// May not always work as toArray() returns a promise,
// which may not be ready for use.
result.forEach((x,i) => console.log('student #' + String(i) + ': ' + x["fname"] + ' ' + x["lname"]))

result.forEach((x,i) => console.log('student #' + String(i+1) + ': ' + x["fname"] + ' ' + x["lname"]))

result = db.student.find({"major": "CINF"},
   { "fname": 1, "lname":1, "major": 1, "minor": 1, "_id": 0 }  
).toArray()


result.forEach((x,i) => console.log('student #' + String(i+1) + ': ' + x["fname"] + 
	' ' + x["lname"] + ' major in ' + x["major"]))


// [5] Show the names and credits (ach) of students majoring in 'CSCI' and having 40 or more credits.

db.student.find(
   { "major": "CSCI", "ach" : {$gte: 40} },
   { "fname": 1, "lname":1, "ach":1, "_id": 0 }  
)

// [6] Show the first name and last name of students with a first name starting with a L or B, case insensitive.
db.student.find(
   { "fname": { $regex: /^[lb]/, $options: "i" } },
   { "fname": 1, "lname":1, "_id": 0 }  
)

// [7] Show the names and credits (ach) of students majoring in 'CSCI' and having 40 or more credits.
db.student.find(
   { "$and": [ { "major": "CSCI"}, { "ach": {"$gte": 40}} ] },
   { "fname": 1, "lname":1, "ach":1, "_id": 0 }  
)


//[9] Show the names of students who have enrolled in 10000: joining two document.

This should have the similar effect of the SQL statement:
SELECT DISTINCT s.fname, s.lname
FROM student AS s, enroll AS e
WHERE s.stuId = e.stuId AND e.classId = 10000;
In MongoDB:
db.student.aggregate([
{$lookup:
    {
      from: "enroll",
      let: {joinValue: '$stuId'},
      pipeline: [
           { $match:
                 { $expr:
                    { $and:
                       [
                         { $eq: [ "$stuId",  "$$joinValue" ] },
                         { $eq: [ "$classId", 10000 ] }
                       ]
                    }
                 }
            }    
        ],
        as: "enrollment"     }},
  { $match: {"enrollment":  { $ne: [] }}},  
  { $project: { "fname": 1, "lname": 1, "_id": 0}} 
])


use tinker
db.test1.insertOne(
   {
      "StudentId" :1,
      "StudentName" : "Joseph Connor"
   }
)

db.test1.find()

db.test1.find({}, { _id: 0 })