I am very new to both Go and Mongodb and was writing my first rest-api with Go and Mongo. I am using mongo-go-driver and have the following Modal struct in Go
type Modal struct {
Group []string `bson:"group" json:"group"`
Hostname string `bson:"hostname" json:"hostname"`
Overrides map[string]string `bson:"overrides" json:"overrides"`
Excludes []string `bson:"excludes" json:"excludes"`
}
I do not want to use the default ObjectId field provided by mongo-db as my primary key and instead would like to make the Hostname field as the primary key.
If I make the type of Hostname field as primitive.ObjectID, then the hostname would be unique but its value will be randomly generated string by mongodb and not the actual hostname string value.
So is there a way I can do this.
You may use a unique index to enforce / allow only distinct values of a given field, e.g.:
db.collectionname.createIndex( { "hostname": 1 }, { unique: true } )
If you want to create such index using the official MongoDB driver, this is how you can do that:
indexName, err := coll.Indexes().CreateOne(
context.Background(),
mongo.IndexModel{
Keys: bson.D{{Key: "hostname", Value: 1}},
Options: options.Index().SetUnique(true),
},
)
But know that in MongoDB each document must have an _id property, so doing the above, documents will have an auto-generated _id field (of ObjectId type). If this doesn't bother you, you're done.
Also note that you may map Modal.Hostname to the _id field with struct tags:
type Modal struct {
Group []string `bson:"group" json:"group"`
Hostname string `bson:"_id" json:"hostname"`
Overrides map[string]string `bson:"overrides" json:"overrides"`
Excludes []string `bson:"excludes" json:"excludes"`
}
And again, you're done. The downside of this solution is that the documents in MongoDB will not have a property named hostname, as it will be stored in _id.
Related
Need some help to figure out why nested bson.M doesn’t work occasionally in FindOne().
For the following Golang structs stored in a MongoDb collection for type A:
type A struct {
Id primitive.ObjectID
Random1 string
Parents []B
Random2 int
}
type B struct {
Id primitive.ObjectID
Random3 string
Children []C
Random4 int
}
type C struct {
Random5 string
Name Name
Random6 int
}
type Name struct {
FirstName string
LastName string
}
The following filter for FindOne(), which uses two bson.M, worked in most situations but failed to find a match in about 10% runs
filter1 := bson.M{
"parents.0.chilren.0.name": bson.M{
"first_name": "Mike",
"last_name": "Anderson",
},
}
The following two filters alway work, where filter 2 uses bson.D inside bson.M, and filter 3 just uses one bson.M
filter2 := bson.M{
"parents.0.chilren.0.name": bson.D{
{Key: "first_name", Value: "Mike"},
{Key: "last_name", Value: "Anderson"},
},
}
filter3 := bson.M{
"parents.0.chilren.0.name.first_name": "Mike",
"parents.0.chilren.0.name.last_name": "Anderson",
}
I found a similar question in https://jira.mongodb.org/browse/GODRIVER-877 but still don’t understand the differences or root cause. Thanks for the help!
bson.M is a map, thus, the order of its elements are not guaranteed. Since you are comparing parents.0.chilren.0.name, which is a structure, the search criteria has to match exactly, with the order of fields in the criteria matching the order fields in the database. That's why when you use bson.M, it sometimes matches and sometimes not. When the search criteria matches the database field order, you get results, otherwise you don't.
That's the reason why the criteria with bson.D always matches, because it is based on a slice, so the order of fields are preserved.
The last search criteria compares individual fields, not a structure, so the order of fields are immeterial.
How can I filter fields with the mongo-go-driver.
Tried it with findopt.Projection but no success.
type fields struct {
_id int16
}
s := bson.NewDocument()
filter := bson.NewDocument(bson.EC.ObjectID("_id", starterId))
var opts []findopt.One
opts = append(opts, findopt.Projection(fields{
_id: 0,
}))
staCon.collection.FindOne(nil, filter, opts...).Decode(s)
In the end, I want to suppress the field "_id". But the documents didn't change.
Edit: As the mongo-go driver evolved, it is possible to specify a projection using a simple bson.M like this:
options.FindOne().SetProjection(bson.M{"_id": 0})
Original (old) answer follows.
The reason why it doesn't work for you is because the field fields._id is unexported, and as such, no other package can access it (only the declaring package).
You must use a field name that is exported (starts with an uppercase latter), e.g. ID, and use struct tags to map it to the MongoDB _id field like this:
type fields struct {
ID int `bson:"_id"`
}
And now to perform a query using a projection:
projection := fields{
ID: 0,
}
result := staCon.collection.FindOne(
nil, filter, options.FindOne().SetProjection(projection)).Decode(s)
Note that you may also use a bson.Document as the projection, you don't need your own struct type. E.g. the following does the same:
projection := bson.NewDocument(
bson.EC.Int32("_id", 0),
)
result := staCon.collection.FindOne(
nil, filter, options.FindOne().SetProjection(projection)).Decode(s)
While working with Mongo Go Driver I want to retrieve Schemaless Documents.
I am able to retrieve documents using bson.M json:",inline" bson:",inline"
But this adds extra "M" key in json when i try to Decode to a struct
type Product struct {
ID primitive.ObjectID `bson:"_id"`
ProductId string `bson:"product_id" json:"product_id"`
bson.M `json:",inline" bson:",inline"`
}
Output:-
{
"id":"<ObjectId>",
"M":{
"some":""
}
}
But instead what i want how it is stored in Mongo.
{
"id":"<ObjectId>",
"some":""
}
I cant use directly something like this as I want to cast it to struct to work with some properties
var pr bson.M
err := p.FindOne(ctx, &p.options,query, &pr)
How can I remove that extra key which is getting added while converting schemaless Documents from Mongo?
Do I need to explicitly overwrite MarshalJSON() or is there something provided using Tags?
How can I remove that extra key which is getting added while converting schemaless Documents from Mongo?
You can just define a field mapping name, which will be flattened when marshalled. For example:
type Product struct {
ID primitive.ObjectID `bson:"_id"`
ProductId string `bson:"product_id"`
Others bson.M `bson:",inline"`
}
When you decode a document, you'll see that it will include other fields without the Others name. For example if you have a document:
{
"_id": ObjectId("5e8d330de85566f5a0557ea4"),
"product_id": "foo",
"some": "x",
"more": "y"
}
doc := Product{}
err = cur.Decode(&doc)
fmt.Println(doc)
// Outputs
// {ObjectID("5e8d330de85566f5a0557ea4") foo map[more:y some:x]}
I cant use directly something like this as I want to cast it to struct to work with some properties
You can use this directly for a query predicate. For example:
// After decoding 'doc' to product
var result bson.M
err := collection.FindOne(context.TODO(), doc).Decode(&result)
Tested using MongoDB Go driver v1.3.2
UPDATED:
If you would like to return JSON, you could use bson.MarshalExtJSON(). This should be easier as well in terms of dealing with objects that don't exist in JSON. i.e. ObjectId. For example:
// After decoding 'doc' to product
ejson, err := bson.MarshalExtJSON(doc, true, false)
fmt.Println(string(ejson))
How can I filter fields with the mongo-go-driver.
Tried it with findopt.Projection but no success.
type fields struct {
_id int16
}
s := bson.NewDocument()
filter := bson.NewDocument(bson.EC.ObjectID("_id", starterId))
var opts []findopt.One
opts = append(opts, findopt.Projection(fields{
_id: 0,
}))
staCon.collection.FindOne(nil, filter, opts...).Decode(s)
In the end, I want to suppress the field "_id". But the documents didn't change.
Edit: As the mongo-go driver evolved, it is possible to specify a projection using a simple bson.M like this:
options.FindOne().SetProjection(bson.M{"_id": 0})
Original (old) answer follows.
The reason why it doesn't work for you is because the field fields._id is unexported, and as such, no other package can access it (only the declaring package).
You must use a field name that is exported (starts with an uppercase latter), e.g. ID, and use struct tags to map it to the MongoDB _id field like this:
type fields struct {
ID int `bson:"_id"`
}
And now to perform a query using a projection:
projection := fields{
ID: 0,
}
result := staCon.collection.FindOne(
nil, filter, options.FindOne().SetProjection(projection)).Decode(s)
Note that you may also use a bson.Document as the projection, you don't need your own struct type. E.g. the following does the same:
projection := bson.NewDocument(
bson.EC.Int32("_id", 0),
)
result := staCon.collection.FindOne(
nil, filter, options.FindOne().SetProjection(projection)).Decode(s)
I have the following model:
type UserModel struct {
Id string `bson:"_id,omitempty"`
CreatedAt *time.Time `bson:"createdAt,omitempty"`
BasicInfo *UserBasicInfoModel `bson:"basicInfo,omitempty"`
}
// *Embedded document*
type UserBasicInfoModel struct {
FirstName *string `bson:"firstName,omitempty"`
LastName *string `bson:"lastName,omitempty"`
}
I am using pointers, in order to be able to distinguish between a missing value (nil) and default value (eg empty strings, false values etc). I also use omitempty to be able to do partial updates.
When I create a user I get the following (correct) response back:
"id": "aba19b45-5e84-55e0-84f8-90fad41712f6",
"createdAt": "2018-05-26T15:08:56.764453386+03:00",
"basicInfo": {
"firstName": "Initial first name",
"lastName": "Initial last name"
}
When I try to update the document though I have an issue.
I send the changes as a new UserModel, to only change the FirstName field in the embedded document like this:
newFirstName := "New Value"
UserModel{
BasicInfo: &UserBasicInfoModel{
FirstName: &newFirstName,
},
}
The code I use to do the update is the following:
UpdateId(id, bson.M{"$set": changes})
The response I get back is the following:
"id": "aba19b45-5e84-55e0-84f8-90fad41712f6",
"createdAt": "2018-05-26T12:08:56.764Z",
"basicInfo": {
"firstName": "New Value",
"lastName": null
}
The createdAt value is not null (as I expected) however the lastName value is null (which is not what I expected)
I would have expected to get back the following:
"id": "aba19b45-5e84-55e0-84f8-90fad41712f6",
"createdAt": "2018-05-26T12:08:56.764Z",
"basicInfo": {
"firstName": "New Value",
"lastName": "Initial last name"
}
What can I do to achieve a partial update in a subdocument using mgo?
First let's quickly explain your createdAt field. This is the value you save: 2018-05-26T15:08:56.764453386+03:00. Know that MongoDB stores dates with millisecond precision, and in UTC timezone. So this date when saved and retrieved from MongoDB becomes 2018-05-26T12:08:56.764Z, this is the "same" time instant, just in UTC zone and precision truncated to milliseconds.
Now on to updating embedded documents:
The short and unfortunate answer is that we can't do this directly with the mgo library and Go models.
Why?
When we use the ,omitempty option, and we leave some pointer fields at their zero value (that is, being nil), it's like if we were using a value whose type didn't even have those fields.
So in your example, if you only change the BasicInfo.FirstName field, and you use this value to update, it is equivalent to using these structures:
type UserModel struct {
Id string `bson:"_id,omitempty"`
BasicInfo *UserBasicInfoModel `bson:"basicInfo,omitempty"`
}
type UserBasicInfoModel struct {
FirstName *string `bson:"firstName,omitempty"`
}
So the effect of your issued update command will be the following:
db.users.update({_id: "aba19b45-5e84-55e0-84f8-90fad41712f6"},
{$set:{
"_id": "aba19b45-5e84-55e0-84f8-90fad41712f6",
"basicInfo": {
"firstName": "New Value"
}
}}
)
What does this mean? To set the _id to the same value (it won't change), and to set the basicInfo field to an embedded document which only has a single firstName property. This will erase the lastName field of the embedded basicInfo document. So when you unmarshal the document after the update into a value of your UserModel type, the LastName field will remain nil (because it is not present in MongoDB anymore).
What can we do?
Flatten the embedded document
One trivial solution is to not use an embedded document, but add fields of UserBasicInfoModel to UserModel:
type UserModel struct {
Id string `bson:"_id,omitempty"`
CreatedAt *time.Time `bson:"createdAt,omitempty"`
FirstName *string `bson:"firstName,omitempty"`
LastName *string `bson:"lastName,omitempty"`
}
Hybrid with ,inline option
This solution keeps the separate Go struct, but in MongoDB it will not be an embedded document (BasicInfo will be flattened just like in the previous example):
type UserModel struct {
Id string `bson:"_id,omitempty"`
CreatedAt *time.Time `bson:"createdAt,omitempty"`
BasicInfo UserBasicInfoModel `bson:"basicInfo,omitempty,inline"`
}
Note that BasicInfo needs to be a non-pointer if ,inline is used. This is not a problem, as we can leave it being an empty struct if its fields are not to be changed, since its fields are pointers, so leaving them nil will not change them.
Doing "manual" update
If you do need to use embedded document, the mgo library allows you to update specific fields of embedded documents, but then you have to "manually" construct the update document, like in this example:
c.UpdateId(Id, bson.M{"$set": bson.M{
"basicInfo.firstName": newFirstName,
}})
Yes, this isn't convenient at all. If you do need this many times with different types, you may create a utility function that uses reflection, iterates over the fields recursively, and assemble the update document from fields which are not nil. Then you could pass that dynamically generated update doc to UpdateId() for example.