For a given fair A, it's major category are a set of its cat.major subdocuments.
For example, for the fair:
{ cat: [ { major: "abc", minor: [ 1,23,3] }, { major: "xyz", minor: [ 3, 23, 583]} ] }
its major categories are set ["abc, "xyz"].
Here we say the major categories of fair X is majorCat(X).
If the intersection of set majorCat(X) and majorCat(Y) are not empty,
we say fair X and Y are related.
So for a given fair X, how to find all its related fairs in a collection?
Here is the demonstration:
In mongodb, create a test collection with the following codes:
db.cats.insert( { cat: [ { major: "abc", minor: [ 1,23,3] }, { major: "xyz", minor: [ 3, 23, 583]} ] } );
db.cats.insert( { cat: [ { major: "abcd", minor: [ 1,23,3] }, { major: "xyzu", minor: [ 87, 987, 343]} ] } );
db.cats.insert( { cat: [ { major: "bcd", minor: [ 1,23,3] }, { major: "abc", minor: [ 3, 23, 876]} ] } );
db.cats.insert( { cat: [ { major: "xyz", minor: [ 8,83,5] }, { major: "axc", minor: [ 34, 3, 76]} ] } );
Create a new Meteor app with meteor create relatedFairs, and its files:
relatedFairs.html
<head>
<title>relatedFairs</title>
</head>
<body>
<h1>Find related fairs</h1>
{{> hello}}
</body>
<template name="hello">
<ul>
{{#each allFairs}}
<li>
<b>{{_id._str}}:</b>
{{#each cat}}
{{major}},
{{/each}}
</li>
{{/each}}
</ul>
{{#with related}}
<p>Related fairs of the first fair {{firstID}}</p>
<ul>
{{#each relatedFairs}}
<li>
<b>{{_id._str}}:</b>
{{#each cat}}
{{major}},
{{/each}}
</li>
{{/each}}
</ul>
{{/with}}
</template>
relatedFairs.js:
Fairs = new Mongo.Collection("cats");
if (Meteor.isClient) {
Template.hello.helpers({
allFairs: function () {
return Fairs.find();
},
related: function () {
var theXrd = 0,
theFair = Fairs.findOne( {}, {skip: theXrd } );
if (! theFair) {
return null;
}
var majors = _.map(theFair.cat, function(i) { return i.major; } );
var rels = Fairs.find( { cat: { $elemMatch: { major: { $in: majors } } },
_id: { $ne: theFair._id } } );
return {firstID: theFair._id._str, relatedFairs: rels };
}
});
}
Here we use Underscore.js,
so install this package with meteor add underscore to run our demo app
(with MONGO_URL="mongodb://localhost:27017/test" meteor in project root folder).
Modify the value of "theXrd" above, you can see the related fairs of each fair.
To make a demo in a production collection, in fair "A" we find a major category called "垃圾车与运输车"， then choose a fair B, whose id is "54e71a5642fb549b1389ae6f".
Let's add the major cateory to fair B:
db.fairs.update( { _id: ObjectId("54e71a5642fb549b1389ae6f") }, { $push: {category: {major: "垃圾车与运输车"}} } );
Now fair A and B is related. Test them on your web site. If the test is past, remove the test data from fair B:
db.fairs.update( { _id: ObjectId("54e71a6642fb549b1389ae6f") }, { $pop: { category: 1 } } );