Added code example.

Author: Arjan Egges

1_basic_app.py

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+from enum import Enum
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Category(Enum):
+    TOOLS = 'tools'
+    CONSUMABLES = 'consumables'
+
+
+class Item(BaseModel):
+    name: str
+    price: float
+    count: int
+    id: int
+    category: Category
+
+
+items = {
+    0: Item(name="Hammer", price=9.99, count=20, id=0, category=Category.TOOLS),
+    1: Item(name="Pliers", price=5.99, count=20, id=1, category=Category.TOOLS),
+    2: Item(name="Nails", price=1.99, count=100, id=2, category=Category.CONSUMABLES),
+}
+
+
+# FastAPI handles JSON serialization and deserialization for us.
+# We can simply use built-in python and Pydantic types, in this case dict[int, Item].
+@app.get("/")
+def index() -> dict[str, dict[int, Item]]:
+    return {"items": items}

1_main.py

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+import requests
+
+print(requests.get("http://127.0.0.1:8000/").json())

2_creating_get_route_query.py

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+from enum import Enum
+
+from pydantic import BaseModel
+
+from fastapi import FastAPI, HTTPException
+
+app = FastAPI()
+
+
+class Category(Enum):
+    TOOLS = "tools"
+    CONSUMABLES = "consumables"
+
+
+class Item(BaseModel):
+    name: str
+    price: float
+    count: int
+    id: int
+    category: Category
+
+
+items = {
+    0: Item(name="Hammer", price=9.99, count=20, id=0, category=Category.TOOLS),
+    1: Item(name="Pliers", price=5.99, count=20, id=1, category=Category.TOOLS),
+    2: Item(name="Nails", price=1.99, count=100, id=2, category=Category.CONSUMABLES),
+}
+
+
+@app.get("/")
+def index() -> dict[str, dict[int, Item]]:
+    return {"items": items}
+
+
+# Path parameters can be specified with {} directly in the path (similar to f-string syntax)
+# These parameters will be forwarded to the decorated function as keyword arguments.
+@app.get("/items/{item_id}")
+def query_item_by_id(item_id: int) -> Item:
+    if item_id not in items:
+        HTTPException(status_code=404, detail=f"Item with {item_id=} does not exist.")
+
+    return items[item_id]
+
+
+# Function parameters that are not path parameters can be specified as query parameters in the URL
+# Here we can query items like this /items?count=20
+Selection = dict[
+    str, str | int | float | Category | None
+]  # dictionary containing the user's query arguments
+
+
+@app.get("/items/")
+def query_item_by_parameters(
+    name: str | None = None,
+    price: float | None = None,
+    count: int | None = None,
+    category: Category | None = None,
+) -> dict[str, Selection | list[Item]]:
+    def check_item(item: Item):
+        """Check if the item matches the query arguments from the outer scope."""
+        return all(
+            (
+                name is None or item.name == name,
+                price is None or item.price == price,
+                count is None or item.count != count,
+                category is None or item.category is category,
+            )
+        )
+
+    selection = [item for item in items.values() if check_item(item)]
+    return {
+        "query": {"name": name, "price": price, "count": count, "category": category},
+        "selection": selection,
+    }

2_main.py

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+import requests
+
+print(requests.get("http://127.0.0.1:8000/items/1").json())
+print(requests.get("http://127.0.0.1:8000/items?name=Nails").json())

3_main.py

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+import requests
+
+print("Adding an item:")
+print(
+    requests.post(
+        "http://127.0.0.1:8000/",
+        json={"name": "Screwdriver", "price": 3.99, "count": 10, "id": 4},
+    ).json()
+)
+print(requests.get("http://127.0.0.1:8000/").json())
+print()
+
+print("Updating an item:")
+print(requests.put("http://127.0.0.1:8000/update/0?count=9001").json())
+print(requests.get("http://127.0.0.1:8000/").json())
+print()
+
+print("Deleting an item:")
+print(requests.delete("http://127.0.0.1:8000/delete/0").json())
+print(requests.get("http://127.0.0.1:8000/").json())

3_more_routing.py

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+from enum import Enum
+
+from pydantic import BaseModel
+
+from fastapi import FastAPI, HTTPException
+
+app = FastAPI()
+
+
+class Category(Enum):
+    TOOLS = "tools"
+    CONSUMABLES = "consumables"
+
+
+class Item(BaseModel):
+    name: str
+    price: float
+    count: int
+    id: int
+    category: Category
+
+
+items = {
+    0: Item(name="Hammer", price=9.99, count=20, id=0, category=Category.TOOLS),
+    1: Item(name="Pliers", price=5.99, count=20, id=1, category=Category.TOOLS),
+    2: Item(name="Nails", price=1.99, count=100, id=2, category=Category.CONSUMABLES),
+}
+
+
+@app.get("/")
+def index() -> dict[str, dict[int, Item]]:
+
+    return {"items": items}
+
+
+@app.get("/items/{item_id}")
+def query_item_by_id(item_id: int) -> Item:
+
+    if item_id not in items:
+        HTTPException(status_code=404, detail=f"Item with {item_id=} does not exist.")
+
+    return items[item_id]
+
+
+Selection = dict[
+    str, str | int | float | Category | None
+]  # dictionary containing the user's query arguments
+
+
+@app.get("/items/")
+def query_item_by_parameters(
+    name: str | None = None,
+    price: float | None = None,
+    count: int | None = None,
+    category: Category | None = None,
+) -> dict[str, Selection | list[Item]]:
+    def check_item(item: Item):
+        """Check if the item matches the query arguments from the outer scope."""
+        return all(
+            (
+                name is None or item.name == name,
+                price is None or item.price == price,
+                count is None or item.count != count,
+                category is None or item.category is category,
+            )
+        )
+
+    selection = [item for item in items.values() if check_item(item)]
+    return {
+        "query": {"name": name, "price": price, "count": count, "category": category},
+        "selection": selection,
+    }
+
+
+@app.post("/")
+def add_item(item: Item) -> dict[str, Item]:
+
+    if item.id in items:
+        HTTPException(status_code=400, detail=f"Item with {item.id=} already exists.")
+
+    items[item.id] = item
+    return {"added": item}
+
+
+@app.put("/update/{item_id}")
+def update(
+    item_id: int,
+    name: str | None = None,
+    price: float | None = None,
+    count: int | None = None,
+) -> dict[str, Item]:
+
+    if item_id not in items:
+        HTTPException(status_code=404, detail=f"Item with {item_id=} does not exist.")
+    if all(info is None for info in (name, price, count)):
+        raise HTTPException(
+            status_code=400, detail="No parameters provided for update."
+        )
+
+    item = items[item_id]
+    if name is not None:
+        item.name = name
+    if price is not None:
+        item.price = price
+    if count is not None:
+        item.count = count
+
+    return {"updated": item}
+
+
+@app.delete("/delete/{item_id}")
+def delete_item(item_id: int) -> dict[str, Item]:
+
+    if item_id not in items:
+        raise HTTPException(
+            status_code=404, detail=f"Item with {item_id=} does not exist."
+        )
+
+    item = items.pop(item_id)
+    return {"deleted": item}

4_main.py

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+import requests
+
+# These requests work:
+print(requests.get("http://127.0.0.1:8000/items?count=20").json())
+print(requests.get("http://127.0.0.1:8000/items?category=tools").json())
+
+
+# This request fails because 'ingredient' is not a valid category, as defined in the Category enum:
+print(requests.get("http://127.0.0.1:8000/items?category=ingredient").json())
+
+
+# These request fail because count has to be an integer:
+
+# Here, validation occurs because of the specified type hints on the endpoint.
+print(requests.get("http://127.0.0.1:8000/items/?count=Hello").json())
+
+# And here, because of Pydantic.
+print(
+    requests.post(
+        "http://127.0.0.1:8000/",
+        json={"name": "Screwdriver", "price": 3.99, "count": 'Hello', "id": 4},
+    ).json()
+)
+
+