improve openai embeddings (#351)

add more formal support for explicitly specifying each model, but in a
backwards compatible way

langchain/embeddings/openai.py

@@ -22,9 +22,8 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
     """
 
     client: Any  #: :meta private:
-    model_name: str = "babbage"
-    """Model name to use."""
-
+    document_model_name: str = "text-embedding-ada-002"
+    query_model_name: str = "text-embedding-ada-002"
     openai_api_key: Optional[str] = None
 
     class Config:
@@ -32,6 +31,26 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
 
         extra = Extra.forbid
 
+    # TODO: deprecate this
+    @root_validator(pre=True)
+    def get_model_names(cls, values: Dict) -> Dict:
+        """Get model names from just old model name."""
+        if "model_name" in values:
+            if "document_model_name" in values:
+                raise ValueError(
+                    "Both `model_name` and `document_model_name` were provided, "
+                    "but only one should be."
+                )
+            if "query_model_name" in values:
+                raise ValueError(
+                    "Both `model_name` and `query_model_name` were provided, "
+                    "but only one should be."
+                )
+            model_name = values.pop("model_name")
+            values["document_model_name"] = f"text-search-{model_name}-doc-001"
+            values["query_model_name"] = f"text-search-{model_name}-query-001"
+        return values
+
     @root_validator()
     def validate_environment(cls, values: Dict) -> Dict:
         """Validate that api key and python package exists in environment."""
@@ -66,7 +85,7 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
             List of embeddings, one for each text.
         """
         responses = [
-            self._embedding_func(text, engine=f"text-search-{self.model_name}-doc-001")
+            self._embedding_func(text, engine=self.document_model_name)
             for text in texts
         ]
         return responses
@@ -80,7 +99,5 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
         Returns:
             Embeddings for the text.
         """
-        embedding = self._embedding_func(
-            text, engine=f"text-search-{self.model_name}-query-001"
-        )
+        embedding = self._embedding_func(text, engine=self.query_model_name)
         return embedding