func NewKey(c appengine.Context, kind, stringID string, intID int64, parent *Key) *Key
The documentation says :
NewKey creates a new key. kind cannot be empty. Either one or both of stringID and intID must be zero. If both are zero, the key returned is incomplete. parent must either be a complete key or nil.
What is the zero for string?
I tried 0 and nil, and I got errors like:
cannot use nil as type string in function argument
转载于:https://stackoverflow.com/questions/12703243/what-is-the-zero-for-string
That's "" :
var s string
fmt.Println(s=="") // prints "true"
A string cannot be nil (but a *string can).
You can simply test
if stringId=="" {
To pass a zero string in stringID, use
k := NewKey(c, "kind", "", 0, p)
From the specification :
When memory is allocated to store a value, either through a declaration or a call of make or new, and no explicit initialization is provided, the memory is given a default initialization. Each element of such a value is set to the zero value for its type: false for booleans, 0 for integers, 0.0 for floats, "" for strings, and nil for pointers, functions, interfaces, slices, channels, and maps.
var str string
fmt.Println(str == "")
put above into your script, and go run it.
you can get the true, golang's string default value is "".
in this case empty string, or you can use NewIncompleteKey()