| relation db | mongodb | |
|---|---|---|
| data structure | tabular format | hierarchy format - like xml |
| whole data | table | association |
| db record | row | document in json format |
| one record item | column | key-value pair |
| join 2 tables | left outer join, add additional columns if available. |
combining two associations, add additional key-value pair if available. |
var MongoClient = require('mongodb').MongoClient
var url = "mongodb://localhost:27017/mydb"
MongoClient.connect(url, function(err, db) {
if (err) throw err;
console.log('after connect the mongodb')
db.close()
console.log('after close the connection to the mongodb')
})
review mongo client api methods signature
for example: MongoClient.connect(url, function(err, db) {...})
notes:
1. connect method is needed for mongo client.
2. When using mongo shell command, the server and the db client are in the same network tier.
3. A nodejs app and the db are two different network tiers.
4. The second method argument is a callback function.
5. This is an asynchronously call.
6. When the db task is completed, the callback is called with data or error message.
7. Other api, like find, findOne, remove, insert, insertOne follow the same function pattern.
8. This is a functional programming feature.
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/mydb";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
// action 1
db.collection("tablexyz").remove() {
if (err) throw err;
console.log("tablexyz is removed.");
})
// other actions
db.close() // close db
}) // end of connect
// insert the following code after remove
// 2. insert one document into a collection
var myobj = { property_id: 17071501, address: "Green ave 37, Canton, MA" };
db.collection("tablexyz").insertOne(myobj, function(err, res) {
if (err) throw err
console.log("1 record inserted");
}) // end of insertOne
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/mydb";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
// remove
db.collection("propertyList").remove() // delete all rows
// insert many documents
var myobjects =
[
{ property_id: 17071601, address: "Jordon St 11, f1" },
{ property_id: 17071602, address: "Jordon St 11, f2" },
{ property_id: 17071603, address: "Jordon St 12, f1" },
{ property_id: 17071604, address: "Jordon St 12, f2" }
]
db.collection("propertyList").insert(myobjects, function(err, res) {
if (err) throw err;
console.log("3 documents inserted")
}) // end of insert
db.close()
}) // end of connect
db.collection("propertyList").find().toArray(function(err, result) {
if (err) throw err
console.log(result) // all documents in json array
console.log(result[0]) // one document from one array item
console.log(result[1].address) // one item's property
})
db.collection("propertyList").find()
.sort({property_id: 1})
.toArray(function(err, result) {
if (err) throw err
console.log(result)
})
db.collection("propertyList").find( {}, {address: 1, _id: 0)
.sort({property_id: 1})
.toArray(function(err, result) {
if (err) throw err
console.log(result)
})
// code to insert table property -------------------
var myobjects =
[
{ id: 17071604, price: 300000, status: "sales pending" },
{ id: 17071603, price: 350000, status: "on sale"},
{ id: 17071601, price: 320000, status: "sold"}
]
db.collection("properties").insert(myobjects, function(...){...}
// application js code -----------------------------
db.collection('propertyList').aggregate(
[
{
$lookup: // nodejs operator
{
from: 'properties',
localField: 'property_id',
foreignField: 'id',
as: 'property_details'
}
}
],
function(err, res) { //join result
if (err) throw err
console.log(res) // output the result for study purpose
// loop result array for study purpose
for (var i = 0; i < res.length; i++){
// get one propertydata
var pdata = res[i].property_details[0]
if (pdata){
var s = res[i].property_details[0].status
var p = res[i].property_details[0].price
console.log("status = " + s + ", price = " + p)
}
}
1. If you see the test result, property document is [[Object]] or [].
That is why I use loop to examine the data.
I believe that in real code, you can wait until you try to use the join result.
2. For the type of table property with [[ ]], I follow the sample code.
When you try to get data, simply follow the model.
} // end of function
} // end of aggregate
// test result ----------------------------------------
[ { _id: 596bd0e6c6cbd2ef6d21d16a,
property_id: 17071604,
address: 'Jordon St 12, f2',
property_details: [ [Object] ] }, // from the 2nd table
{ _id: 596bd0e6c6cbd2ef6d21d16b,
property_id: 17071603,
address: 'Jordon St 12, f1',
property_details: [ [Object] ] }, // from the 2nd table
{ _id: 596bd0e6c6cbd2ef6d21d16c,
property_id: 17071602,
address: 'Jordon St 11, f2',
property_details: [] }, // no data from the 2nd table
{ _id: 596bd0e6c6cbd2ef6d21d16d,
property_id: 17071601,
address: 'Jordon St 11, f1',
property_details: [ [Object] ] } ] // from the 2nd table
status = sales pending, price = 300000
status = on sale, price = 350000
status = sold, price = 320000
// 1. get one ducument find(query, projection) from w3c-nodejs-mongodb
var query = { id: 17071604 }
db.collection("properties").find(query).toArray(function(err, result) {
if (err) throw err
console.log("result = " + result) // [object object]
console.log("price = " + result[0].price) // 300000
}) // end toArray
// 2. update one document, updateOne(filter, update,options)
// from mongodb web site
// $set is nodejs operator
// verify the result, using find method
try {
db.collection('properties').updateOne(
{ id : 17071604 },
{ $set: { price : 299000 } }
) // end of updateOne
console.log("one document updated")
} catch (e) {
print(e)
}
// 3. delete one document, deleteOne(filter,...)
// from mongodb web site
// $eq is nodejs operator
// verify the result, using find method, the document(status is sold) is removed. no longer needed.
try {
db.collection("properties").deleteOne( { "status" : { $eq: 'sold' } } )
console.log("one document deleted")
} catch (e) {
print(e)
}