I'm using the mongo-go driver for Go to save some documents on mongoDb. Everyhting works fine, but i'm wondering if there is a way to change how the ID is auto-generated. Right now the document model in the code has the primitive.ObjectID type, is something like this
type Review struct {
ID primitive.ObjectID `json:"id,omitempty" bson:"_id,omitempty"`
Title string `json:"title"`
Text string `json:"text"`
Rate float64 `json:"rate"`
Date time.Time `json:"date"`
Product Product `json:"product"`
}
And the document created is something like this
{
"_id" : ObjectId("5d6f739a20d42db438016cb1"),
"title" : "test-id",
"text" : "rev-text",
"rate" : 5.0,
"date" : ISODate("2019-09-02T12:18:00.000+02:00"),
"status" : "pending"
}
So far so good. However i want the ID to be a UUID, not an ObjectId. I know i can change the struct ID type to UUID or string and set that field when i'm saving the document, however i want to know if there is a way to change the default ObjectID generator of mongoDb so it generates a UUID automatically when saving a new document
You don't have to use an ObjectID for _id:
ID string `json:"id,omitempty" bson:"_id,omitempty"`
Then you can insert any value you want for _id. However, you won't be able to auto-generate ID this way, you have to generate the ID yourself, and insert it with the generated ID.
Related
I have the following model:
type Drink struct {
gorm.Model // Adds some metadata fields to the table
ID uuid.UUID `gorm:"type:uuid;primary key"`
Name string `gorm:"index;not null;"`
Volume float64 `gorm:"not null;type:decimal(10,2)"`
ABV float64 `gorm:"not null;type:decimal(10,2);"`
Price float64 `gorm:"not null;type:decimal(10,2);"`
Location Location `gorm:"ForeignKey:DrinkID;"`
}
type Location struct {
gorm.Model // Adds some metadata fields to the table
ID uuid.UUID `gorm:"primary key;type:uuid"`
DrinkID uuid.UUID
Name string `gorm:"not null;"`
Address string `gorm:"not null;type:decimal(10,2)"`
Phone int `gorm:"not null;type:decimal(10,0);"`
}
however, when I run the program, it adds both tables, however there is no location field in the Drink table.
My database looks like this after the migrations, regardless of whether I drop the tables previously:
I have a sneaking feeling it might be because I am not using the gorm default ID, but if that's the case can anyone point me to how to override the default ID with a UUID instead of a uint the proper way? or if that's not even the issue, please, I've been working on this for a few days now and I really don't want to take the "easy" road of just using the defaults gorm provides, I actually want to understand what is going on here and how to properly do what I am trying to do. I am getting no errors when running the API, and the migration appears to run as well, it's just the fields I have defined are not actually showing up in the database, which means that the frontend won't be able to add data properly.
What I WANT to happen here is that a list of stores will be available in the front-end, and when a user adds a drink, they will have to select from that list of stores. Each drink added should only have 1 store, as the drinks prices at different stores would be different. So technically there would be many "repeated" drinks in the drink table, but connected to different Locations.
First point is as you are using custom primary key, you should not use gorm.Model as it contains ID field in it. Reference
Second point is according to your description, store (location) has one to
many relationship with drink. That means a store can have multiple
drinks but a drink should belong to only one store. In one-to-many
relationship there should be a reference or relation id in the many
side. That means in your case in drink table. Then your struct
should look like this:
MyModel Struct
type MyModel struct {
CreatedAt time.Time
UpdatedAt time.Time
DeletedAt gorm.DeletedAt `gorm:"index"`
}
Location Struct (Store)
type Location struct {
MyModel
ID uuid.UUID `gorm:"primary key;type:uuid"`
// other columns...
Drinks []Drink
}
Drink Struct
type Drink struct {
MyModel
ID uuid.UUID `gorm:"type:uuid;primary key"`
//other columns...
LocationID uuid.UUID// This is important
}
Then gorm will automatically consider LocationID in drink table will be referring the ID field of Location Table. You can also explicitly instruct this to gorm using gorm:"foreignKey:LocationID;references:ID" in Location struct's Drinks array field.
Reference
I am trying to use the official mongodb driver in golang and am seeing something unexpected.
If I have a struct like
type User struct {
ID primitive.ObjectID `json:"id" bson:"_id"`
Name string `json:"name" bson:"name"`
Email string `json:"email" bson:"email"`
}
I create a new instance of this with Name and Email but omit ID expecting that the DB will fill this with its value. Instead it uses all zeroes and so the second and so on inserts fail with
multiple write errors: [{write errors: [{E11000 duplicate key error collection: collection.name index: _id_ dup key: { : ObjectId('000000000000000000000000') }}]}, {<nil>}]
If I use a *primitive.ObjectID I get the same class of error only on null instead of zeroes
multiple write errors: [{write errors: [{E11000 duplicate key error collection: collection.name index: _id_ dup key: { : null }}]}, {<nil>}]
It doesn't matter if I use the omitempty directive or not, same result.
If I omit the ID field entirely, it works, but then my struct doesn't have that data on it.
Is there a way to have the DB handle the ID? Or MUST I explicitly call the NewObjectID() function on the struct?
It doesn't matter if I use the omitempty directive or not, same result.
omitempty tag on ID should work. For example:
type User struct {
ID primitive.ObjectID `json:"id" bson:"_id,omitempty"`
Name string `json:"name" bson:"name"`
Email string `json:"email" bson:"email"`
}
collection.InsertOne(context.Background(), User{Name:"Foo", Email:"Baz"})
If you don't specify the omitepmty tag, then the behaviour that you observed is just Go structs behaviour; whereby if any of struct fields are omitted it will be zero-valued. In this case because you have specified the field type to be primitive.ObjectID, ObjectId('000000000000000000000000') is the zero value.
This is the reason why you need to generate a value first before inserting, i.e.:
collection.InsertOne(context.Background(),
User{ ID: primitive.NewObjectID(),
Name: "Foo",
Email: "Bar"})
Is there a way to have the DB handle the ID?
Technically, it's the MongoDB driver that automatically generates the ObjectId if it's not supplied before sending to server.
You can try to use bson.M instead of a struct when inserting to leave out the _id field, i.e.
collection.InsertOne(context.Background(),
bson.M{"name":"Foo", "email":"Bar"})
Code snippet above is written using mongo-go-driver v1.3.x
The omitempty struct tag should work:
type User struct {
ID primitive.ObjectID `json:"id" bson:"_id,omitempty"`
Name string `json:"name" bson:"name"`
Email string `json:"email" bson:"email"`
}
The primitive.ObjectID type implements the bsoncodec.Zeroer interface, so it should be omitted from the document if it's the empty object ID (all 0's) and the driver will generate a new one for you. Can you try this and post the output?
Suppose we have the following struct:
type shop struct {
ID primitive.ObjectID `json:"_id,omitempty" bson:"_id,omitempty"`
Brands *brand `json:"brand,omitempty" bson:"brand,omitempty"`
}
type brand struct {
ID primitive.ObjectID `json:"_id,omitempty" bson:"deploymentid,omitempty"`
}
I tried to find a document using findOne() but I don't get any document even there is a result match by using the MongoDB shell.
filter := bson.M{"brand" : bson.M{"_id" : someValue}}
var shopWithBrand shop
mycollection.findOne(ctx , filter).Decode(&shopWithBrand)
What mistake did I make?
This filter:
filter := bson.M{"brand" : bson.M{"_id" : someValue}}
Tells you want documents that have a brand field that is an embedded document having a single _id field whose value is the value of someValue.
This would actually work if your embedded documents would only consist of this single _id field, but your embedded brand has this ID field mapped to deploymentid and most likely has other fields as well (which you "stripped off" to minimize the example), and that is why it won't match.
Instead you want documents that have a brand field being a document that has a matching deployment field among other fields. This is how you can express that:
filter := bson.M{"brand.deploymentid" : someValue}
I'm very new to golang and try to write a simple event-sourcing user-management webapi using mongodb as backing database. Now i have User, which looks something like this:
type User struct {
Id bson.ObjectId `json:"id" bson:"_id"`
UserName string `json:"username" bson:"username"`
Email string `json:"email" bson:"email"`
PwdHash string `json:"pwd_hash" bson:"pwd_hash"`
FullName string `json:"fullname" bson:"fullname"`
}
and three events, happening to user, when somebody uses api:
type UserCreatedEvent struct {
UserId bson.ObjectId `json:"id" bson:"_id"`
//time when event was issued
CreatedEpoch time.Time `json:"created_epoch" bson:"created_epoch"`
//id of user that made a change
IssuedByUserId bson.ObjectId `json:"issuedby_userid" bson:"issuedby_userid"`
}
type UserDeletedEvent struct {
UserId bson.ObjectId `json:"id" bson:"_id"`
CreatedEpoch time.Time `json:"created_epoch" bson:"created_epoch"`
//id of user that made a change
IssuedByUserId bson.ObjectId `json:"issuedby_userid" bson:"issuedby_userid"`
}
type UserUpdatedEvent struct {
UserId bson.ObjectId `json:"id" bson:"_id"`
CreatedEpoch time.Time `json:"created_epoch" bson:"created_epoch"`
//id of user that made a change
IssuedByUserId bson.ObjectId `json:"issuedby_userid" bson:"issuedby_userid"`
ChangedFieldName string `json:"changed_field_name" bson:"changed_field_name"`
NewChangedFieldValue string `json:"new_changed_field_value" bson:"new_changed_field_value"`
}
Now i'm stuck on saving and retrieving events from db. The problem is i want to store them in a single collection, so that i have a full plain history of user modifications. But i can't find how to correctly store event type name as a mongo document field and then use it in searches. What is the idiomatic go-way to do this?
I'll be gratefull for any help.
What's nice about a non-relational database is that a little redundancy is OK and is faster for retrieval since you're not joining things together. You could just add your bottom three objects as properties on your User in whatever fashion makes sense for you and your data. Then you wouldn't need to store the UserId on those objects either.
If you need to search over the Events quickly, you could create another collection to hold them. You'd be inserting to two collections, but retrieval times/logic should be pretty good/easy to write.
Your new Event would be something like:
type UserEventType int
const (
Created UserEventType = iota
Deleted
Updated
)
type UserEvent struct {
UserId bson.ObjectId `json:"id" bson:"_id"`
CreatedEpoch time.Time `json:"created_epoch" bson:"created_epoch"`
//id of user that made a change
IssuedByUserId bson.ObjectId `json:"issuedby_userid" bson:"issuedby_userid"`
ChangedFieldName string `json:"changed_field_name,omitempty" bson:"changed_field_name,omitempty"`
NewChangedFieldValue string `json:"new_changed_field_value,omitempty" bson:"new_changed_field_value,omitempty"`
EventType UserEventType `json:"user_event_type" bson:"user_event_type"`
}
Notice the omitempty on the fields that are optional depending on the type of event.
You really aren't supposed to store different objects in the same collection. Here's a line from the Mongo documentation:
MongoDB stores documents in collections. Collections are analogous to tables in relational databases.
In case you aren't familiar with relational databases, a table would essentially represent one type of object.
I have the following document in my local mongodb:
_id 25dd9d29-efd5-4b4e-8af0-360c49fdba31
name Reykjavik
initialDiseaseColouring blue
In my code I set up a city structure as the following:
type City struct {
ID bson.ObjectId `bson:"_id,omitempty"`
Name string
InitialDiseaseColouring string
}
I'm querying it using
result := City{}
collection.Find(bson.M{"name":"Reykjavik"}).One(&result)
When I try to access the initialDiseaseColouring attribute it's not there
This is result when I print it:
{ObjectIdHex("32356464396432392d656664352d346234652d386166302d333630633439666462613331") Reykjavik }
Does anyone know why?
I was following the example on https://gist.github.com/border/3489566
By default, the bson codec uses the lowercased field name as the key. Use the field tag to specify a different key:
type City struct {
ID bson.ObjectId `bson:"_id,omitempty"`
Name string
InitialDiseaseColouring string `bson:"initialDiseaseColouring"`
}
The addition of the field tag changes the key from "initialdiseasecolouring" to "initialDiseaseColouring".