How to Automatically Populate `created_at` and `updated_at` Fields in Go Structs Before MongoDB Insertion?

Autofill created_at and updated_at in Go Struct Before Inserting into MongoDB

When inserting a struct into a MongoDB collection using the MongoDB driver for Go, the created_at and updated_at fields are set to the zero time (0001-01-01T00:00:00.000 00:00). This may not be the desired behavior, especially if these fields are expected to store the actual time of creation and modification.

Custom Marshaler

The MongoDB server does not natively support auto-populating created_at and updated_at fields. However, you can implement this functionality by creating a custom marshaler.

Implementing bson.Marshaler

Implement the bson.Marshaler interface for your User type. This will allow you to customize how the struct is marshaled into BSON before being inserted into the database.

The MarshalBSON method of your custom marshaler should perform the following steps:

1. If CreatedAt is zero, set it to the current time.
2. Set UpdatedAt to the current time.
3. Marshal the struct into BSON using the base bson.Marshal function.

Here's an example of a custom marshaler:

func (user *User) MarshalBSON() ([]byte, error) {
    if user.CreatedAt.IsZero() {
        user.CreatedAt = time.Now()
    }
    user.UpdatedAt = time.Now()

    type my User
    return bson.Marshal((*my)(user))
}

Usage

To use the custom marshaler, remember to use it wherever you insert a User struct into the database using the InsertOne method. You must pass a pointer to the User struct as an argument.

Example:

user := &User{Name: "username"}

c := client.Database("db").Collection("collection")
if _, err := c.InsertOne(context.Background(), user); err != nil {
    // handle error
}

Note that the custom marshaler will not work if you embed it into a larger struct. To avoid this issue, you can use a custom marshaler for the entire embedded struct instead.

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