Develop Reference

Which data model structure to use in Postgres?

I am quite new to using databases and have only used MongoDB so far. I was planning on making a app for a shop to create their menu(s).
There are several interfaces I would define beforehand.
interface FoodItem {
id: number
name: string,
price: number
}
interface Category {
id: number,
name: string,
food: FoodItem[]
}
interface Menu {
id: number
name:string,
categories: Category[]
}
From the above schemas, I was wondering if this is ok for a Postgres database, where all the data resides in the Menus table, and fetching a Menu will yield all nested Categories and FoodItems.
I am confused because from other examples of such data models, the array of Categories will simply be replaced by an array of IDs that points to their respective Categories and the same for FoodItems as well. In that case, to fetch a Menu, the database will also have to fetch, say 3 other Categories and in those categories fetch another say 10 other FoodItems via their IDs. Wouldn't that be a performance issue since the database has to query each nested item in the array, as opposed to doing it all in one single query fetch from the root Menu?
For my app that I'm designing, each Category and FoodItem is unique to their parents and will not be shared with other Categories/Menus. In that case there wouldn't be duplicate entries of FoodItem when using the first data model. Of course I would not mind using the second data model since it is much cleaner and easy to reference without deeply nested objects.
So for the second data model, would there a big performance decrease when my dataset starts to grow larger and larger?

How to index referenced field in firebase?

I have a "products" collection:
products:{
PD1232:{
name:"Brick",
type: LPK52
},
PD553: {
name:"Panel",
type: DX343
}
}
The products collection is referenced to a "lookup" collection:
productTypes:{
LPK52:{
name: "Concrete mixed with dried bamboo"
},
DX343: {
name: "bla bla........"
}
}
In terms of searching the products, I want to index the "products" collection as a whole. It means I want to also combine a collection and its referenced collection when indexing. So for example when I search with the term "Concrete mixed with dried bamboo", it also returns the respective product as a result (the one with uid=LPK52). Please give me the solution?

You can first search for product types by name ("Concrete mixed with dried bamboo") and that will give you type IDs, then search for products by type ("LPK52"). I am not aware of any shortcuts.
Or, if you're willing to maintain it when you edit a type, you can add a typeName field in your products and search directly in them by typeName.

There is no way to search in one collection and get results from another collection.
One option is to do what Stratubas describes: first find the product types matching your condition, then find the products for that type.
If you don't want to do that, you can consider duplicating the product type name into each product document as a field. That would allow you to immediately query on products based on their product type's name.

Meteor Collections and when to use a schema

I am starting to build an app and have a collection that is used to create a pet post.
Note: I'm using the following packages to build my collection schemas, Simple Schema https://atmospherejs.com/aldeed/simple-schema
The page that I'm using to insert the data into this particular collection has a section that based on the choice the user makes they are presented with more options.
For example focusing in on one question there are some checkboxes, by default none are selected but if the user selects any checkbox they are given more options to choose from either via checkboxes or text areas. The point is that they will have additional options to choose from based on their selection.
I think the best way to handle how the data is inserted is via the template helpers for that specific section so that's not the question.
Instead where i'm confused is at the collection level and how to Schema that information or if I even need to.
For example let's say you have a question that involves pets.
The question could be: Do you have pets?
The checkbox options could be:
Dogs
Cats
Other
By default all of these checkboxes are unchecked but if the user checks any of the boxes then a text area is revealed (again i realize all of this happens at the Template.events and Template.helpers level).
What my real question is, now that I've set the scenario, is how do you store information like that or schema it to allow these kinds of values.
Assuming that all of the functions to grab this data are all on the Template.helpers level so this is simple a question about how to store kind of data in this scenario.
My notion was to do something like this (using the simpleSchema package):
Pet = new SimpleSchema({
petInstructions: {
type: String,
optional: true,
allowedValues: ['Dogs', 'Cats', 'Other']
}
});
However I'm not certain this is right again let me re-iterate that I do want the checkboxes to have the values 'Dogs', 'Cats', 'Other' and the text area when any of these are checked so that the end-user can enter more information about their pets.
What i'm unclear about is if I'm thinking about how this data's Schema could be or how this kind of information should be stored in the MongoDB.
I feel like there should also be a property for the TextArea input, would that be a good way to think about it?
For example (adding on to the example above):
Pet = new SimpleSchema({
petInstructions: {
type: String,
optional: true,
allowedValues: ['Dogs', 'Cats', 'Other'],
textArea: ""
}
});
Should I just leave another property/value for that particular content?
This is somewhat of a granular level question that understanding something simple like this would help clarify other questions I had.
Thank you.

This is how I would structure it. This is from the autoform instructions for how to validate a field against another field and how to conditionally require a value - https://github.com/aldeed/meteor-simple-schema#best-practice-code-examples
Pet = new SimpleSchema({
pet: {
type: Object,
optional: true
},
"pet.type": {
type: String,
optional: true,
allowedValues: ['Dogs', 'Cats', 'Other']
},
"pet.instructions": {
type: String,
optional: true,
custom: function(){
var petType = this.field('pet.type').value;
// if the user selects a pet type then instructions should be required
if (petType){
return "required";
};
}
}
});
In your old code:
Pet = new SimpleSchema({
petInstructions: {
type: String,
optional: true,
allowedValues: ['Dogs', 'Cats', 'Other'],
textArea: ""
}
});
You are literally stating that for the petInstructions key, you only allow the values to be Dogs, Cats, or Other, but you also want one of the keys to be textArea with some other data, which doesn't make too much sense. SimpleSchema wants you to define a specific data point for each key.

Get part of a list effectively with Mongoose

I have a schema like this.
peopleSchema = Schema({
followerRefs: {
type: [
{ type: Schema.Types.ObjectId, ref: 'peoples'}
],
select: false
},
followRefs: {
type: [
{ type: Schema.Types.ObjectId, ref: 'peoples'}
],
select: false
}
});
Every time, I just want to select part of the followerRefs or followRefs. For example, I want to implement a paging, so I just want to select first 20 in the followRefs, or first 21 ~ 40 in the followRefs.
So, are there any way to get part of the followerRefs with select all of the list?
It seems that I didn't explain my question clearly. I assume that there are over one million entity in the followerRefs in database, and I just want to get the first 20 of them, which mean I just want to get the index of 0~19 of them. So I don't want to load all of the one million entity into the memory.
So I'm wondering whether there are any way to get the first 20 entity without load all of them?

If it's just a list of names, I don't think you should handle the sorting via mongoose nor the backend.
But it depends on the size of data still.
Via javascript(frontend) I would sort the list first depending on what category, then I'd sort it.
Sorting with plain javascript could be complicated and I'm not an expert with it, since I use plugins. XD
So here's a link with a link with an answer about javascript sorting.
Sorting an array of JavaScript objects
Since you are asking about parts of the array, just use javascript slice() function.
var myList = ["Follower1", "Follower2", "Follower3", ...]; //pretend it goes til 20
var page1 = myList.slice(0, 19);

Mongoose - recursive query (merge from multiple results)

I have the following generic schema to represent different types of information.
var Record = new Schema (
{
type: {type: String}, // any string (foo, bar, foobar)
value: {type: String}, // any string value
o_id: {type:String}
}
);
Some of the records based on this schema have:
type="car"
value="ferrari" or
value="ford"
Some records have type "topspeed" with value "210" but they always share o_id (e.g. related "ferrari has this topspeed"). So if "ferrari has top speed 300", then both records have same o_id.
How can I make query to find "ferrari with topspeed 300" when I don't know o_id?
The only solution I found out is to select cars "ferrari" first and then with knowledge of all o_id for all "ferrari" use it to find topspeed.
In pseudocode:
Record.find({type:"car", value:"ferrari"}, function(err, docs)
{
var condition = [];// create array of all found o_id;
Record.find({type:"topspeed", value:"300"}...
}
I know that some merging or joining might not be possible, but what about some chaining these conditions to avoid recursion?
EDIT:
Better example:
Lets imagine I have a HTML document that contains DIV elements with certain id (o_id).
Now each div element can contain different type of microdata items (Car, Animal...).
Each microdata item has different properties ("topspeed", "numberOfLegs"...) based on the type (Car has a topspeed, animal numberOfLegs)
Each property has some value (310 kph, 4 legs)
Now I'm saving these microdata items to the database but in a general way, agnostic of the type and values they contain since the user can define custom schemas from Car, to Animal, to pretty much anything). For that I defined the Record schema: type consists of "itemtype_propertyname" and value is value of the property.
I would eventually like to query "Give me o_id(s) of all DIV elements that contain item Ferrari and item Dog" at the same time.
The reason for this general approach is to allow anyone the ability to define custom schema and corresponding parser that stores the values.
But I will have only one search engine to find all different schemas and value combinations that will treat all possible schemas as a single definition.

I think it'd be far better to combine all records that share an o_id into a single record. E.g.:
{
_id: ObjectId(...),
car: "ferarri",
topspeed: 300
}
Then you won't have this problem, and your schema will be more efficient both in speed and storage size. This is how MongoDB is intended to be used -- heterogenous data can be stored in a single collection, because MongoDB is schemaless. If you continue with your current design, then no, there's no way to avoid multiple round-trips to the database.