openai: WithEmbeddingModel option is incorrectly designating the desi…

…red model to use for embedding (#731)

* chore: issue #729

* chore: issue #729

examples/openai-embeddings-example/openai-embeddings-example.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+
+	"github.com/tmc/langchaingo/llms/openai"
+)
+
+func main() {
+	opts := []openai.Option{
+		openai.WithModel("gpt-3.5-turbo-0125"),
+		openai.WithEmbeddingModel("text-embedding-3-large"),
+	}
+	llm, err := openai.New(opts...)
+	if err != nil {
+		log.Fatal(err)
+	}
+	ctx := context.Background()
+	embedings, err := llm.CreateEmbedding(ctx, []string{"ola", "mundo"})
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(embedings)
+}

llms/openai/internal/openaiclient/embeddings.go

@@ -34,13 +34,19 @@ type embeddingResponsePayload struct {
 
 // nolint:lll
 func (c *Client) createEmbedding(ctx context.Context, payload *embeddingPayload) (*embeddingResponsePayload, error) {
+	if c.baseURL == "" {
+		c.baseURL = defaultBaseURL
+	}
+
+	if c.apiType == APITypeOpenAI {
+		payload.Model = c.embeddingsModel
+	}
+
 	payloadBytes, err := json.Marshal(payload)
 	if err != nil {
 		return nil, fmt.Errorf("marshal payload: %w", err)
 	}
-	if c.baseURL == "" {
-		c.baseURL = defaultBaseURL
-	}
+
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.buildURL("/embeddings", c.embeddingsModel), bytes.NewReader(payloadBytes))
 	if err != nil {
 		return nil, fmt.Errorf("create request: %w", err)