Initial implementation of request cache

connectors/reqcache/reqcache.go

@@ -0,0 +1,181 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package reqcache
+
+import (
+	"context"
+
+	"github.com/uber-go/dosa"
+	"github.com/uber-go/dosa/connectors/base"
+	"github.com/uber-go/dosa/connectors/memory"
+)
+
+type cacheKey string
+
+// ReqCacheKey is the key used for the context request cache.
+// Best practice is to use a private type to avoid any possible collisions
+const ReqCacheKey = cacheKey("reqcache")
+
+// Connector is the request cache connector type.
+type Connector struct {
+	base.Connector
+}
+
+// NewConnector constructs a request context connector
+func NewConnector(db dosa.Connector) *Connector {
+	return &Connector{base.Connector{db}}
+}
+
+// CacheableContext produces a context that has a cache in it
+// from one that does not
+func CacheableContext(ctx context.Context) context.Context {
+	cache := memory.NewConnector()
+	return context.WithValue(ctx, ReqCacheKey, cache)
+}
+
+func cacheFromContext(ctx context.Context) dosa.Connector {
+	rc := ctx.Value(ReqCacheKey)
+	if rc == nil {
+		return nil
+	}
+	if conn, ok := rc.(dosa.Connector); ok {
+		return conn
+	}
+	return nil
+}
+
+// CreateIfNotExists creates the object downstream, then upserts it into the local cache
+// when successful
+func (c *Connector) CreateIfNotExists(ctx context.Context, ei *dosa.EntityInfo, values map[string]dosa.FieldValue) error {
+	err := c.Next.CreateIfNotExists(ctx, ei, values)
+	if err == nil {
+		if cache := cacheFromContext(ctx); cache != nil { // if there is a cache
+			_ = cache.Upsert(ctx, ei, values) // then update it
+		}
+	}
+	return err
+}
+
+// Read reads first from the cache, and if not present, will read from the downstream
+// connector
+func (c *Connector) Read(ctx context.Context, ei *dosa.EntityInfo, values map[string]dosa.FieldValue, minimumFields []string) (map[string]dosa.FieldValue, error) {
+	cache := cacheFromContext(ctx)
+	if cache != nil {
+		// cache present, attempt to read from it
+		vals, err := cache.Read(ctx, ei, values, minimumFields)
+
+		if err == nil {
+			return vals, nil
+		}
+	}
+	// cache not present or is missing the value, read it from the db
+	vals, err := c.Next.Read(ctx, ei, values, dosa.All())
+	// stash it in case it is read again
+	if cache != nil {
+		_ = cache.Upsert(ctx, ei, vals)
+	}
+
+	return vals, err
+}
+
+// MultiRead is not implemented
+func (c *Connector) MultiRead(ctx context.Context, ei *dosa.EntityInfo, keys []map[string]dosa.FieldValue, minimumFields []string) (results []*dosa.FieldValuesOrError, err error) {
+	panic("not implemented")
+}
+
+// Upsert first writes to the upstream and, if successful, will
+// update the object in the cache
+func (c *Connector) Upsert(ctx context.Context, ei *dosa.EntityInfo, values map[string]dosa.FieldValue) error {
+	err := c.Next.Upsert(ctx, ei, values)
+	if err == nil {
+		if cache := cacheFromContext(ctx); cache != nil { // if there is a cache
+			// TODO: this doesn't work correctly for partial updates unless it was already cached
+			_ = cache.Upsert(ctx, ei, values)
+		}
+	}
+	return err
+}
+
+// MultiUpsert is not implemented
+func (c *Connector) MultiUpsert(ctx context.Context, ei *dosa.EntityInfo, multiValues []map[string]dosa.FieldValue) (result []error, err error) {
+	panic("not implemented")
+}
+
+// Remove removes the item from the remote database, and, if successful,
+// removes it from the cache
+func (c *Connector) Remove(ctx context.Context, ei *dosa.EntityInfo, keys map[string]dosa.FieldValue) error {
+	err := c.Next.Remove(ctx, ei, keys)
+	if err == nil {
+		if cache := cacheFromContext(ctx); cache != nil { // if there is a cache
+			_ = cache.Remove(ctx, ei, keys)
+		}
+	}
+	return err
+}
+
+// RemoveRange removes a range from the datastore, and, if successful,
+// removes it from the cache
+func (c *Connector) RemoveRange(ctx context.Context, ei *dosa.EntityInfo, columnConditions map[string][]*dosa.Condition) error {
+	err := c.Next.RemoveRange(ctx, ei, columnConditions)
+	if err == nil {
+		if cache := cacheFromContext(ctx); cache != nil {
+			_ = cache.RemoveRange(ctx, ei, columnConditions)
+		}
+	}
+	return err
+}
+
+// MultiRemove is not implemented
+func (c *Connector) MultiRemove(ctx context.Context, ei *dosa.EntityInfo, multiKeys []map[string]dosa.FieldValue) (result []error, err error) {
+	panic("not implemented")
+}
+
+// Range reads from the upstream datasource, and, if successful, updates
+// the cache for each object returned by range
+func (c *Connector) Range(ctx context.Context, ei *dosa.EntityInfo, columnConditions map[string][]*dosa.Condition, minimumFields []string, token string, limit int) ([]map[string]dosa.FieldValue, string, error) {
+	vals, token, err := c.Next.Range(ctx, ei, columnConditions, dosa.All(), token, limit)
+
+	if err == nil {
+		if cache := cacheFromContext(ctx); cache != nil {
+			// if there is a cache, insert each found value into the cache
+			for _, v := range vals {
+				_ = cache.Upsert(ctx, ei, v)
+			}
+		}
+	}
+	return vals, token, err
+}
+
+// Search is not implemented
+func (c *Connector) Search(ctx context.Context, ei *dosa.EntityInfo, fieldPairs dosa.FieldNameValuePair, minimumFields []string, token string, limit int) (multiValues []map[string]dosa.FieldValue, nextToken string, err error) {
+	panic("not implemented")
+}
+
+// Scan currently just defers to the downstream for scanning
+// It does not update the request cache.
+func (c *Connector) Scan(ctx context.Context, ei *dosa.EntityInfo, minimumFields []string, token string, limit int) (multiValues []map[string]dosa.FieldValue, nextToken string, err error) {
+	return c.Next.Scan(ctx, ei, minimumFields, token, limit)
+}
+
+// Shutdown shuts down the connector
+func (c *Connector) Shutdown() error {
+	return c.Next.Shutdown()
+}