Appending Data to an Interface Pointing to a Defined Struct using 'reflect' - mongodb

Question

I am trying to create a function where it gets all the documents from a Mongo Collection and queries them to declared structs. To achieve this I set the parameters for the function of type interface so it can work with two structs. Here is my code:
In package entities:
type Project struct {
Title string
Position string
....
}
type Projects struct {
Projects []Project
}
In the current package:
var docs entities.Projects
var doc entities.Project
//doc represents a document from Mongo Collection
//docs represents an array of documents, each element is a document
//collection has type *mongo.Collection and points to the desired collection on MongoDB.
createQuery(&doc, &docs, collection)
func createQuery(doc interface{}, docs interface{}, c *mongo.Collection) {
documents := reflect.ValueOf(docs).Elem()
document := reflect.ValueOf(doc)
cur, err := c.Find(context.Background(), bson.D{{}})
if err != nil {
log.Fatal(err)
}
for cur.Next(context.Background()) {
err = cur.Decode(document.Interface())
if err != nil {
log.Fatal(err)
}
//Error is thrown here
documents.Set(reflect.Append(documents, document))
fmt.Println(doc)
}
if err := cur.Err(); err != nil {
log.Fatal(err)
}
if err != nil {
fmt.Printf("oh shit this is the error %s \n", err)
}
cur.Close(context.Background())
fmt.Printf("documents: %+v\n", documents.Interface())
fmt.Printf("document: %+v\n", document.CanSet())
}
---ERROR OUTPUT---
panic: reflect: call of reflect.Append on struct Value
I was able to set data to doc using the document variable, although when doing document.CanSet() is false (so it may not even work). Where the program breaks is when I try to append the document to the documents interface.

Answer 1

The code in the question passes the struct docs to a function that expects a slice. Pass the address of the slice field in docs instead of docs itself.
The createQuery function can determine the slice element type from the slice itself. There's no need to pass in an example value.
var docs entities.Projects
createQuery(&docs.Projects, collection)
for _, doc := range docs.Projects {
fmt.Println(doc.Title)
}
The call to cur.Decode requires a pointer to an uninitialized value. Use reflect.New to create that value.
func createQuery(docs interface{}, c *mongo.Collection) {
docsv := reflect.ValueOf(docs).Elem()
doct := docsv.Type().Elem()
cur, err := c.Find(context.Background(), bson.D{{}})
if err != nil {
log.Fatal(err)
}
for cur.Next(context.Background()) {
docpv := reflect.New(doct)
err = cur.Decode(docpv.Interface())
if err != nil {
log.Fatal(err)
}
docsv.Set(reflect.Append(docsv, docpv.Elem()))
}
if err := cur.Err(); err != nil {
log.Fatal(err)
}
cur.Close(context.Background())
}
As an aside, the entities.Projects struct type is not needed if that struct type will only ever have one field. Use []Project instead:
var docs []entities.Project
createQuery(&docs, collection)
for _, doc := range docs {
fmt.Println(doc.Title)
}