Merge pull request #81 from JohnMaguire/context-documentation

Add some notes about the context parameter

Author: pavelnikolov

README.md

@@ -9,7 +9,8 @@ This is an implementation of [Facebook's DataLoader](https://github.com/facebook
 
 ## Usage
 ```go
-// setup batch function
+// setup batch function - the first Context passed to the Loader's Load
+// function will be provided when the batch function is called.
 batchFn := func(ctx context.Context, keys dataloader.Keys) []*dataloader.Result {
   var results []*dataloader.Result
   // do some async work to get data for specified keys
@@ -26,6 +27,10 @@ loader := dataloader.NewBatchedLoader(batchFn)
  * A thunk is a function returned from a function that is a
  * closure over a value (in this case an interface value and error).
  * When called, it will block until the value is resolved.
+ *
+ * loader.Load() may be called multiple times for a given batch window.
+ * The first context passed to Load is the object that will be passed
+ * to the batch function.
  */
 thunk := loader.Load(context.TODO(), dataloader.StringKey("key1")) // StringKey is a convenience method that make wraps string to implement `Key` interface
 result, err := thunk()

dataloader.go

@@ -190,7 +190,9 @@ func NewBatchedLoader(batchFn BatchFunc, opts ...Option) *Loader {
 	return loader
 }
 
-// Load load/resolves the given key, returning a channel that will contain the value and error
+// Load load/resolves the given key, returning a channel that will contain the value and error.
+// The first context passed to this function within a given batch window will be provided to
+// the registered BatchFunc.
 func (l *Loader) Load(originalContext context.Context, key Key) Thunk {
 	ctx, finish := l.tracer.TraceLoad(originalContext, key)