I want to implement lazy loading in angular.js, i am sending the list of data from backend to the UI using nodejs, i need to implement, on scroll 10 items, are there any examples to achieve this please share any links to do this. Please can anybody help me on this.
Lazy loading is nothing to do with DB, since it depends on the DAO layer, whereas DB is concerned about returning the data for the query submitted to it.
My approach to achieve lazy loading from UI
Using pagination we can do lazy loading
1) Find the total number of documents in your collection
2) Each time when you are loading the page with next set of data, pass on the required information such as from which document the DB needs to send the data
3) Repeat step 2 until you reach the total number of documents in your collection
An example Let us have a collection with few records
db.mycollection.find();
{ "_id" : ObjectId("58947e7e93cbb73057657d60"), "name" : "Clement" }
{ "_id" : ObjectId("58947e7e93cbb73057657d61"), "name" : "Rockin" }
{ "_id" : ObjectId("58947e7e93cbb73057657d62"), "name" : "Gowri" }
{ "_id" : ObjectId("58947e7e93cbb73057657d63"), "name" : "Inbaraj" }
{ "_id" : ObjectId("58947e7e93cbb73057657d64"), "name" : "Siva" }
{ "_id" : ObjectId("58947e7e93cbb73057657d65"), "name" : "Rani" }
{ "_id" : ObjectId("58947e7e93cbb73057657d66"), "name" : "Rose" }
{ "_id" : ObjectId("58947e7e93cbb73057657d67"), "name" : "Rekha" }
{ "_id" : ObjectId("58947e7e93cbb73057657d68"), "name" : "Dev" }
{ "_id" : ObjectId("58947f6f93cbb73057657d69"), "name" : "Joe" }
{ "_id" : ObjectId("58947f8393cbb73057657d6a"), "name" : "Beniton" }
Prerequisite for doing pagination
db.mycollection.find().count()
11
Let me have the initial load size as 5
My first query to DB would be
db.mycollection.find().sort({"_id":1}).limit(5);
{ "_id" : ObjectId("58947e7e93cbb73057657d60"), "name" : "Clement" }
{ "_id" : ObjectId("58947e7e93cbb73057657d61"), "name" : "Rockin" }
{ "_id" : ObjectId("58947e7e93cbb73057657d62"), "name" : "Gowri" }
{ "_id" : ObjectId("58947e7e93cbb73057657d63"), "name" : "Inbaraj" }
{ "_id" : ObjectId("58947e7e93cbb73057657d64"), "name" : "Siva" }
My Next query to DB
db.mycollection.find().sort({"_id":1}).skip(5).limit(5);
{ "_id" : ObjectId("58947e7e93cbb73057657d65"), "name" : "Rani" }
{ "_id" : ObjectId("58947e7e93cbb73057657d66"), "name" : "Rose" }
{ "_id" : ObjectId("58947e7e93cbb73057657d67"), "name" : "Rekha" }
{ "_id" : ObjectId("58947e7e93cbb73057657d68"), "name" : "Dev" }
{ "_id" : ObjectId("58947f6f93cbb73057657d69"), "name" : "Joe" }
final query would be
db.mycollection.find().sort({"_id":1}).skip(10).limit(5);
{ "_id" : ObjectId("58947f8393cbb73057657d6a"), "name" : "Beniton" }
In this example,
Sort on _id is used, which is based on insertion time, which helps us in ordering the documents and render it for the subsequent queries.
Hope it Helps!
References:
https://www.mongodb.com/blog/post/the-mean-stack-mongodb-expressjs-angularjs-and
Lazy Loading/More Data Scroll in Mongoose/Nodejs
http://adrichman.github.io/implementing-a-lazy-load-and-infinite-scroll-in-angularjs/
Related
i have a list schema and a question set schema. the quetsionSet schema is embedded inside the list schema. its working fine but how can i update anything inside the array of embedded document i.e. here i want to change the listname of all the documents inside questionSet (array of questionSet documents).
here is an example of my list document model
{ "_id" : ObjectId("60f2cc07275bbb30d8cb268e"),
"listName" : "dsa",
"aboutList" : "dsa queestions",
questionSet" : [ { "solved" : false,
"_id" : ObjectId("60f2cc12275bbb30d8cb2695"),
"topic" : "array",
"name" : "array is best",
"url" : "www.arr.com",
"listname" : "dsa",
"__v" : 0 },
{ "solved" : false,
"_id" : ObjectId("60f2cc1b275bbb30d8cb269d"),
"topic" : "linked list",
"name" : "reverse list",
"url" : "www.list.com",
"listname" : "dsa",
"__v" : 0 }
],
"__v" : 2
}
you can use the following in your case
db.<collection_name>.updateOne(
{ "_id" : ObjectId("60f2cc07275bbb30d8cb268e")},
{
$set: {
'questionSet.$[].listname': "javascript"
}
}
)
I have a database on firebase where data is inserted, divided into two sections (CAT1, CAT2). This is the structure:
`
{
"mPulHwx4C6eTQEwUhhXXTsGb2eq2" : {
"CAT1" : {
"-LjMnx_GdJt2qQNlh7ko" : {
"id" : 238,
"title" : "FILM1",
"type" : "movie"
}
},
"CAT2" : {
"-LjMo4XjVOlUVnvs_iiw" : {
"id" : 60625,
"title" : "SERIE1",
"type" : "tv"
}
}
}
}
`
How can I delete an item, for example from CAT1, after calling up the entire object via axios?
In MongoDB, I have models of User, Token, and Boost.
A user can have one or more tokens and one or more boosts.
Token has a 2dsphere location field.
And Boost has startTime and stopTime Date fields.
A user is said to have an active boost if Date.now() is greater than boost.startTime() and less than boost.stopTime().
What Mongo aggregation can I write to fetch me all the tokens near a particular location that belong to users with at least one active boost?
Based on your question, I have created a mock data
token collection:
{
"_id" : ObjectId("5b97541c6af22cc65216ffd8"),
"userid" : "5b9753726af22cc65216ffd6",
"location" : {
"longitude" : 80.250875,
"latitude" : 13.052519
}
},
{
"_id" : ObjectId("5b97543a6af22cc65216ffd9"),
"userid" : "5b97537e6af22cc65216ffd7",
"location" : {
"longitude" : 80.249995,
"latitude" : 13.051819
}
}
boost collection :
{
"_id" : ObjectId("5b9754796af22cc65216ffda"),
"startTime" : ISODate("2018-09-11T05:36:57.149Z"),
"stopTime" : ISODate("2018-09-11T05:36:57.149Z"),
"userid" : "5b9753726af22cc65216ffd6"
},
{
"_id" : ObjectId("5b9754b46af22cc65216ffdb"),
"startTime" : ISODate("2018-10-08T18:30:00.000Z"),
"stopTime" : ISODate("2018-10-08T18:30:00.000Z"),
"userid" : "5b97537e6af22cc65216ffd7"
}
Users collection :
{
"_id" : ObjectId("5b9753726af22cc65216ffd6"),
"userName" : "user111"
},
{
"_id" : ObjectId("5b97537e6af22cc65216ffd7"),
"userName" : "user222"
}
The aggregate query to fetch all the tokens near a particular location that belong to users with at least one active boost is:
db.token.aggregate([
{
"$geoNear": {
"near": { type: "Point", coordinates: [80.248797,13.050599] },
"distanceField": "location",
"maxDistance": 1000,
"includeLocs": "location",
"spherical": true
}
},
{"$lookup" : {"from":"boost",
"localField" : "userid",
"foreignField" : "userid",
"as" : "boostDocs"
}},
{"$unwind" : "$boostDocs"},
{"$match" : {"$and":[{"boostDocs.startTime":{"$lte":new Date("11/09/2018")}},{"boostDocs.stopTime":{"$gte":new Date("10/09/2018")}}]}}
])
Notice that query to match the location is at the top of the query as $geoNear will only work if its the first stage of the aggregation pipeline.
The Date that I've used for comparison is just to check if my query works. You can specify your date or Date.now() as per your requirement.
I am trying to get only the ObjectId's from One specific Document that is embedded in the projects Array.
Basically I am trying to make a database that will have users and each user will have there own projects.
Thank you !
db.users.find().pretty()
{
"_id" : ObjectId("5762c0cf2b9a78006373a684"),
"name" : "seq",
"pass" : "seq",
"projects" : [
{
"pid" : ObjectId("5762c0ba2b9a78006373a682"),
"name" : "aaa"
},
{
"pid" : ObjectId("5762c0ba2b9a78006373a683"),
"name" : "bbb"
}
]
}
{
"_id" : ObjectId("5762c28d2b9a78006373a687"),
"name" : "leq",
"pass" : "leq",
"projects" : [
{
"pid" : ObjectId("5762c2892b9a78006373a685"),
"name" : "ccc"
},
{
"pid" : ObjectId("5762c2892b9a78006373a686"),
"name" : "ddd"
}
]
}
let say we want two pids
{"pid" : ObjectId("5762c0ba2b9a78006373a682")} and
{"pid" : ObjectId("5762c2892b9a78006373a686"),}
and only inner documents
so required response should look like:
{
"_id" : ObjectId("5762c0ba2b9a78006373a682"),
"name" : "aaa"
},{
"_id" : ObjectId("5762c2892b9a78006373a686"),
"name" : "ddd"
}
Aggregation framework can manipulate documents, match only needed ones and transform inner structure by project phase:
var match = {
$match : {
"projects.pid" : {
$in : [ObjectId("5762c0ba2b9a78006373a682"),
ObjectId("5762c2892b9a78006373a686")]
}
}
}
var unwind = {
$unwind : "$projects"
};
// now move array objet as top level object
var project = {
$project : {
_id : "$projects.pid",
name : "$projects.name",
// list other fields here
}
}
db.vic.aggregate([match, unwind, match, project])
My mongoDB collection looks like this :
{
"_id" : ObjectId("5070310e0f3350482b00011d"),
"emails" : [
{
"_id" : ObjectId("5070310e0f3350482b000120"),
"_type" : "Email",
"name" : "work",
"email" : "peter.loescher#siemens.com",
"current" : true
}
]
}
and this is the .js code i use to print the contents :
c = db.contacts.findOne( { "emails.email" : { $ne : null } }, { "emails" : 1 } )
print(c._id.toString() + " " + c.emails[0]);
when I try to run this javascript file, it is just displaying the id but not the email array.
output:
5070310e0f3350482b00011d [object bson_object]
but when I try c.emails[0].email is is giving proper result. i.e. peter.loescher#siemens.com
All I need is I want to display the whole emails embedded object.
i.e.
"emails" : [
{
"_id" : ObjectId("5070310e0f3350482b000120"),
"_type" : "Email",
"name" : "work",
"email" : "peter.loescher#siemens.com",
"current" : true
}
]
Where I am going wrong?. Any help would be appreciated.
You need printjson to output a nicely formatted JSON:
printjson(c.emails[0]);
Here it is the documentation.