partial update using mgo

Question

I have the following problem. I need to convert a structure to map[string]interface{} in order to perform an update in database (using mgo as driver for mongodb).

Update

For partially updating a document in mongoDB, the (optimal) solution is to convert to a map and delete the unwanted fields. For converting from struct to map please refer to my other post

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Original Post

I receive the data from client side javascript and write in the my struct model. But I don't want to change/update some fields and thus I need to convert my structure to a map[string]interface{} to delete the unwanted fields.

Converting the structure to json and then to map it's not ok because the field types are not preserved. For example, let the followin structure be an Image model:

type Image struct {
    Name string `json:name`
    Views int `json:views,string`
    Owner string `json:owner`
}

So far so good, but when I receive informations from client(i.e. javascript) the views field is a string. If I convert to a map the json input given from client, then the views field remains a string and the internal representation of this value is changed in database. So next time I read this image from database, the Views field is zeroed (because of it's string representation from database).

Thus I write the json input from client in structure (for proper conversion of Views variable). But the owner value shouldn't change (the one form database). So I need to convert again the structure to a map[string]interface{} and process that map before making the update in database.

Using the json package for this it's not an option, because the string tag from Views field will convert from int to string (when converting to map).

So far I've tried the following function for converting structure to map, and I use reflection package and am a noob with using it. Don't quite understand well the package.

I would be grateful if you would come up with some ideas. Thanks.

Approximation

What about client json -> struct -> json -> map -> database? Quite slow but simple is it? – Oversight

@Oversight that's not a solution because when converting from struct -> json, the views field is converted to string (because of the string tag). Not having the string tag on the views field will cause an error when writing from json to struct. – Approximation

ah sorry, can you do client json -> struct -> xml/gob -> map -> database. Since the tag just apply to json package. – Oversight

I think xml would be the only solution. gob expects to be decoded in the same structure type. I might try xml, but think this is the last solution I would use, it slows alot using so many conversions. Thanks. – Approximation

BTW, are you using mgo package? Why don't you just use update partial? – Oversight

Yes I am using mgo. What update partial? Where? Well the final struct I was going to use it as a partial update... – Approximation

let us continue this discussion in chat – Approximation

Answer 1

The solution can be:
1. client json -> struct -> xml -> map -> database
2. Update partital with $set operator:

collection.Update(bson.M{"_id": id}, bson.M{"$set": bson.M{"name": "new Name"}})

Read more: http://docs.mongodb.org/manual/reference/operator/update/set/
3. Load the document that is going to be updated and store it in a tmp variable. Parse the user input to another variable. Overwrite the values you need to preserve before updating.

Oversight

I used the third solution given by you. Thanks – Approximation

Answer 2

If you are using go.mongodb.org/mongo-driver, you will have to use UpdateOnemethod to update the specific fields. Here is the code

    database := db.Conn.Database("myDatabase")
    coll := database.Collection("myCollection")
    
    filter := bson.M{"_id": bson.M{"$eq": objectHexID}}
    update := bson.M{"$set": bson.M{"useremail": "[email protected]"}}

    updated, err := coll.UpdateOne(ctx, filter, update)

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