diff --git a/main.py b/main.py
index 21ebb31..5372093 100644
--- a/main.py
+++ b/main.py
@@ -1,30 +1,54 @@
 # example from root.cz
 # https://www.root.cz/clanky/validace-dat-v-pythonu-s-vyuzitim-knihovny-pydantic/
-
-from models.User import User, UserNone, UserUnion, UserPositiveInt, UserFieldValidator, UserMaxLength
+from models.address import Address
+from models.character import CharacterModel, CharacterModelOptionalAddress
+from models.user import User, UserNone, UserUnion, UserPositiveInt, UserFieldValidator, UserMaxLength
 
 
 def main():
+
+    # Basic validation
     print("Hello from pydantic-demo!")
-    print(f"{User(name="John", surname="Doe", age=42, registered=True)=}")
-    print(f"{User(name="Adam", surname="Bernau", age=52, registered=True)=}")
-    print(f"{UserNone(name="Adam", surname="Bernau", age=None)=}")
-    print(f"{UserUnion(name="Adam", surname="Bernau", age=None)=}")
-    print(f"{UserUnion(name="Adam", surname="Bernau")=}")
-    print(f"{UserPositiveInt(name="Adam", surname="Bernau")=}")
-    #print(f"{UserPositiveInt(name="Adam", surname="Bernau", age=-50)=}")
-    print(f"{UserFieldValidator(name="Adam", surname="Bernau", age=18)=}")
-    print(f"{UserMaxLength(name="Adam", surname="Bernau", age=18)=}")
-    #print(f"{UserMaxLength(name="Adam", surname="Bernaukjghsmtlmgchs", age=18)=}")
+    print(f"{User(name='John', surname='Doe', age=42, registered=True)=}")
+    print(f"{User(name='Adam', surname='Kameník', age=52, registered=True)=}")
+    print(f"{UserNone(name='Tomáš', surname='Macek', age=None)=}") # preferred variant
+    print(f"{UserUnion(name='Adam', surname='Bernau', age=None)=}")
+    print(f"{UserUnion(name='Adam', surname='Bernau')=}")
+    print(f"{UserPositiveInt(name='Adam', surname='Bernau')=}")
+    #print(f"{UserPositiveInt(name="Adam', surname='Bernau', age=-50)=}")
+    print(f"{UserFieldValidator(name='Adam', surname='Bernau', age=18)=}")
+    print(f"{UserMaxLength(name='Adam', surname='Bernau', age=18)=}")
+    #print(f"{UserMaxLength(name='Adam', surname='Bernaukjghsmtlmgchs', age=18)=}")
 
     # JSON
     data = """
-        {"name": "John",
-         "surname": "Doe",
-         "age": 18
+        {"name": "Marek",
+         "surname": "Kdolský",
+         "age": 50
         }
     """
-    print(f"{UserMaxLength.model_validate_json(data)=}")
+    user1 = UserMaxLength.model_validate_json(data)
+    print(f"{user1=}")
+    print(f"{user1.model_dump_json()=}")
+    print(user1.model_dump_json(indent=4))
+
+    # Nested structure and JSON
+    character = CharacterModel(
+        role='Director',
+        user=User(name='John', surname='Doe', age=42, registered=True),
+        address=Address(street='Dlouhá', house_number=77, city='Prague'),
+    )
+    print(f"{character=}")
+    print(character.model_dump_json(indent=4))
+
+
+    character1 = CharacterModelOptionalAddress(
+        role='Director',
+        user=UserFieldValidator(name='John', surname='Doe', age=19, registered=True),
+        # address=Address(street='Dlouhá', house_number=77, city='Prague'),
+        )
+    print(f"Optional address {character1=}")
+    print(character1.model_dump_json(indent=4))
 
 if __name__ == "__main__":
     main()
diff --git a/models/address.py b/models/address.py
new file mode 100644
index 0000000..caa48d9
--- /dev/null
+++ b/models/address.py
@@ -0,0 +1,9 @@
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Address(BaseModel):
+    street: str
+    house_number:  int | str
+    city: str
diff --git a/models/character.py b/models/character.py
new file mode 100644
index 0000000..44e0ec8
--- /dev/null
+++ b/models/character.py
@@ -0,0 +1,18 @@
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+from models.address import Address
+from models.user import User, UserFieldValidator
+
+
+class CharacterModel(BaseModel):
+    role: str
+    user: User
+    address: Address
+
+class CharacterModelOptionalAddress(BaseModel):
+    role: str
+    user: UserFieldValidator
+    address: Address | None = None
+
diff --git a/models/User.py b/models/user.py
similarity index 78%
rename from models/User.py
rename to models/user.py
index 0e014c8..f4df9f2 100644
--- a/models/User.py
+++ b/models/user.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from typing import Union, Optional
-from pydantic import BaseModel, PositiveInt, field_validator, Field
+from pydantic import BaseModel, PositiveInt, field_validator, Field, ValidationError
 
 
 class User(BaseModel):
@@ -38,24 +38,28 @@ class UserPositiveInt(BaseModel):
 class UserFieldValidator(BaseModel):
     name: str
     surname: str
-    age: PositiveInt | None
+    age: int | None
     registered: bool = False
 
     @field_validator("age")
     def validate_age(cls, value):
+        if value < 0:
+            raise ValidationError("age must be positive")
         if value < 18:
-            raise ValueError("age must be at least 18")
+            raise ValidationError("age must be at least 18")
         return value
 
 
 class UserMaxLength(BaseModel):
     name: str = Field(..., max_length=10)
-    surname: str = Field(..., max_length=10)
-    age: PositiveInt | None
+    surname: str = Field(..., max_length=12)
+    age: int | None
     registered: bool = False
 
     @field_validator("age")
     def check_age(cls, value):
+        if value < 0:
+            raise ValidationError("age must be positive")
         if value < 18:
             raise ValueError("You are too young to register")
         return value