I have a schema that has a field that could reference different schema.
var HistorySchema = new Schema({
type: {type: String, required: true},
objectId: {
type: Schema.Types.ObjectId,
required: true,
},
changed: {type: Schema.Types.Mixed}
})
The documents of this schema allows me to keep track of changes happens in different types of objects with objectId.
For example, if User has changed name from 'John' to 'Steve', a History document would have:
{
type: 'User',
objectId: '55fa6bf0831ba3fa0879e7e8',
changed: {name: {oldValue: 'John', newValue: 'Steve'}}
}
Obviously, type can be many different things.
My question is, can I magically populate the objectId field without knowing type before the query?
I know I can do:
History.query({...}).populate('objectId', null, 'User').exec(...);
But that requires me to know the type is User when the query is constructed.
And obviously I can do a second query manually given the type and objectId.
For example, is it possible to save the ref type of a document (not schema) at runtime and take advantage of that? I look around and don't seem to find a way.
Related
I am using MongoDB via mongooose. Can database references reference two databases at the same time?
field_name: {
type: mongoose.Schema.Types.ObjectId,
ref: 'collectionA',// can I reference collectionA and collectionB too?
required: true,
},
See code above.
The field, field_name, can be an objectId from collectionA or collectionB. How can I reflect that in my mongoose schema?
I guess you are looking for mongoose dynamic reference via refPath.
const someSchema = new Schema({
field_name: {
type: Schema.Types.ObjectId,
required: true,
refPath: 'onCollection'
},
onCollection: {
type: String,
required: true,
enum: ['collectionA', 'collectionB']
}
});
In this case, Instead of a hardcoded model name in ref, refPath means Mongoose
will look at the onCollection property to find the right model.
For example if we have this document:
{
field_name: some_id,
onCollection: 'collectionA'
}
Collection.find().populate('field_name') will populate the field from collectionA. And if the onCollection field was valued with collectionB, it would have populated it from collectionB.
This scenario only works if you want to reference one collection at a time, but the collection is dynamic.
If you need to reference both collections at the same time, there is no mongoose schema design to support array of references as far as I know.
You can just ignore ref in your schema, and pass in the value of ref when you want to populate:
populate({
path: 'field_name',
model: 'collectionA'
})
Then you can have multiple populates. Same applies for $lookup.
I have a following type of schema and I want populate the guide details when getting a tour document. I tried with Tour.findById(id).populate({path: 'summary.guide'}). But in the result it returns a null for guide. How to populate that guide details?
const tourSchema = new mongoose.Schema({
from: String,
to: String,
summary: {
guide: { type: Schema.Types.ObjectId, ref: 'User' },
duration: Number,
distance: Number
}
})
I think you should not pass the user id into the summary.guide object.
The second possibility is user id and summary.guide not match.
The third possibility is summary.guide is not exist.
this code works for me
Tour.findById("5dcd2c61...").populate({path: 'summary.guide'});
I couldn't understand that for what purpose mongoose schemaType is used for. If someone could explain it will be helpful.
I'm have to reference another schema from a schema i want to know if we can get the details of all schema together when we do a findOne() on mongoose.
mixed schema means whatever you want the type to be. if you input a String, Number, Date, mongoose will let you do that. However according to documentation, mongoose ref does not work with mixed.
Note: ObjectId, Number, String, and Buffer are valid for use as refs.
if you use mixed, and ref it, you won't be able to query it back.
If you start all over(delete the database and reinsert again), use ObjectId instead of Mixed.
var storySchema = Schema({
author : { type: ObjectId, ref: 'Person' },
});
If you wish to retain old database, the best way is to change mixed to string
var storySchema = Schema({
author : { type: String, ref: 'Person' },
});
Does Mongoose support, or is there an available package that supports multiple "options" for the embedded schemas in an array?
For example, the things property can contain only one of two schemas:
new Schema({
things: [{
requiredProp: String,
otherProp: Number
}, {
otherOption: Number
}]
});
In other words, I do not want to just allow anything (AKA Schema.Types.Mixed) to be stored in this property, but only these two possible definitions.
Or, do schema design recommendations exist to avoid this problem?
You should only define one dict in the array type of the schema, and then set if they are required or not with the mongoose schema types logic. Use pre save if you want to do more logic to assure that either one of the fields have been set, like this:
var MySchema = new Schema({
things: [{
requiredProp: {type: String, required: true},
otherProp: Number,
otherOption: Number,
}]
});
MySchema.pre('save', function(next) {
if (!this.otherProp && !this.otherOption) {
next(new Error('Both otherProp and otherOption can\'t be null'))
} else {
next()
}
})
Opon saving the object it will return an error if neither otherProp nor otherOption has been set.
I have a simple database in Jaydata:
$data.Entity.extend("Person", {
Name: { type: String, required: true},
LastName: {type: String, required: true},
DepartmentId: {type: int}
});
$data.EntityContext.extend("PersonDatabase", {
People : { type : $data.EntitySet, elementType : Person}
});
var Database1= new PersonDatabase("MyDatabase");
But suppose I don't know the fields of the database I have. Assume I only know the variable Database1 so I need to make a loop which returns column names(fields of "Person"). How can I make that so I can make a dynamic table which can show whatever simple database(#x columns, #y rows) data I will have?
If you have a type in hand for example the Person class, call type.getFieldNames() for and array of public mapped field names (technical fields are not visible). To access each and every field with full metadata consult type.memberDefinitions or type.memberDefinitions.toArray()
The http://admin.jaystack.net site is build with fully generic table routines powered by knockout: check out admin.jaystack.net for an example (you need to register for a free account to access the admin site)