Question

I have an app using Go with this entity:

type Product struct {
  Name string
  Related []*datastore.Key
}

Is this possible to find all products that are related with a given key?

Answer 1

Is this possible to find all products that related with a given key?

As you’re storing a slice of keys, this is not possible without retrieving all entities.

However, you could create a new kind (RelatedProducts) which stores the related products (using the product as parent key).

Example (Not tested)

type Product struct {
    Name string
}
type RelatedProducts struct { // We store the the OriginalProduct as parent, so it is not needed as a property
    Related *datastore.Key
}

// Create a new relation
func newRelation(c appengine.Context, productKey *datastore.Key, relatedProduct *datastore.Key) {
    key := datastore.NewIncompleteKey(c, "RelatedProducts", productKey)
    datastore.Put(c, key, &RelatedProduct{Related: relatedProduct})
}

// Get all related products
func getAllRelatedProducts(c appengine.Context, productKey *datastore.Key) []*datastore.Key{
    var relatedProducts []RelatedProducts

    // Query the relations
    query := datastore.NewQuery("RelatedProducts").Ancestor(productKey)
    query.GetAll(c, &relatedProducts)

    // Loop over relatedProducts and append the data to keys 
    var keys []*datastore.Key
    for i := range relatedProducts {
        keys = append(keys, relatedProducts[i].Related)
    }

    return keys
}