Add details for custom ValueError

README.md

@@ -835,7 +835,7 @@ class Post(BaseModel):
        return creator
     
 # src.posts.router
-@from fastapi import APIRouter, status
+@from fastapi import APIRouter, Depends
 
 router = APIRouter()
 
@@ -892,10 +892,38 @@ class Profile(BaseModel):
     avatar_url: CompanyMediaUrl  # only whitelisted urls for avatar
 
 ```
-### 22. pre if data need to be pre-handled before validation
+### 21. Raise a ValueError in custom pydantic validators, if schema directly faces the client 
-### 23. you can just raise a ValueError in pydantic schemas, if schemas face http client 
+It wil return a nice detailed response to users.
-it wil return a detailed response of the failed fields
+```python
-### 24. don't forget that fastapi converts response Model to Dict then to Model then to JSON
+# src.profiles.schemas
+from pydantic import BaseModel, validator
+
+class ProfileCreate(BaseModel):
+    username: str
+    
+    @validator("username")
+    def validate_bad_words(cls, username: str):
+        if username  == "me":
+            raise ValueError("bad username, choose another")
+        
+        return username
+
+
+# src.profiles.routes
+from fastapi import APIRouter
+
+router = APIRouter()
+
+
+@router.post("/profiles")
+async def get_creator_posts(profile_data: ProfileCreate):
+   pass
+```
+**Response Example:**
+
+<img src="images/custom_bad_response.png" width="400" height="auto">
+
+### 22. don't forget that fastapi converts response Model to Dict then to Model then to JSON
 it may lead to bugs like model can parse only raw data (e.g. forced data aggregation for raw data)
-### 25. if must use sdk, but it's not async, use threadpools
+### 23. if must use sdk, but it's not async, use threadpools
-### 26. use linters (black, isort, autoflake)
+### 24. use linters (black, isort, autoflake)