WIP: Prepare fetch

example/todo/cache.go

@@ -0,0 +1,70 @@
+package todo
+
+import (
+	"context"
+
+	"github.com/99designs/gqlgen/graphql"
+)
+
+type cache struct {
+	requested_ids map[interface{}]struct{}
+	storage       map[interface{}]interface{}
+	loader        loadFunc
+}
+
+type loadFunc func(keys []interface{}) []interface{}
+
+func (c *cache) loadAllRequests() {
+	if c.requested_ids != nil && len(c.requested_ids) > 0 {
+		//collect requested (and missing) id's
+		var ids []interface{}
+		for id := range c.requested_ids {
+			if c.storage[id] == nil {
+				ids = append(ids, id)
+			}
+		}
+		if len(ids) == 0 {
+			return
+		}
+
+		//load missing id's
+		values := c.loader(ids)
+		//store result
+		for i, id := range ids {
+			c.storage[id] = values[i]
+		}
+		//clear
+		c.requested_ids = make(map[interface{}]struct{})
+	}
+}
+
+func (c *cache) getItem(ctx context.Context, id interface{}, loader loadFunc) interface{} {
+	c.loader = loader
+	if c.storage == nil {
+		c.storage = make(map[interface{}]interface{})
+	}
+
+	//preparing?
+	fctx := graphql.GetFieldContext(ctx)
+	if fctx.IsPreparing || (fctx.Parent != nil && fctx.Parent.IsPreparing) {
+		if c.requested_ids == nil {
+			c.requested_ids = make(map[interface{}]struct{})
+		}
+		if _, ok := c.requested_ids[id]; !ok {
+			var empty struct{}
+			c.requested_ids[id] = empty
+		}
+
+		var dummy struct{}
+		return dummy
+	}
+
+	//loading
+	result := c.storage[id]
+	if result == nil {
+		c.loadAllRequests()
+		//load again (from cache now)
+		result = c.storage[id]
+	}
+	return result
+}