add example contract

examples/user_profile.py

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+# =============================================================================
+# MiniChain Storage Paradigms Example: Grouped Values vs Composite Keys
+# =============================================================================
+# 
+# Problem Statement:
+# Unlike Solidity, which allows multiple distinct `mapping` variables,
+# MiniChain provides a single global `storage` dictionary per contract.
+# If you naively try to save an age and a name to the same address key:
+#     storage[sender] = age
+#     storage[sender] = name   <-- This overwrites the age!
+#
+# This contract demonstrates two paradigms to solve this key collision.
+#
+# Valid Payloads:
+# - 'set_grouped:<age>:<name>'
+# - 'update_age_grouped:<new_age>'
+#
+# - 'set_composite:<age>:<name>'
+# - 'update_age_composite:<new_age>'
+# =============================================================================
+
+payload = msg['data']
+sender = msg['sender']
+
+# -----------------------------------------------------------------------------
+# Paradigm 1: Grouped Values
+# -----------------------------------------------------------------------------
+# We store a Python dictionary as the value for the sender's address.
+# Pros: Keeps all user data neatly organized in one object.
+# Cons: To update a single field, we must read the whole dict and write it back.
+
+if payload.startswith('set_grouped:'):
+    parts = payload.split(':')
+    if len(parts) != 3:
+        raise Exception("Invalid format. Use set_grouped:<age>:<name>")
+
+    age = int(parts[1])
+    name = parts[2]
+
+    # Store the entire profile as a single dictionary
+    storage[sender] = {
+        "age": age,
+        "name": name
+    }
+
+elif payload.startswith('update_age_grouped:'):
+    parts = payload.split(':')
+    if len(parts) != 2:
+        raise Exception("Invalid format. Use update_age_grouped:<new_age>")
+
+    new_age = int(parts[1])
+
+    # Notice the inefficiency here: we must load the entire dict,
+    # modify one field, and then re-save the entire dict to storage.
+    profile = storage.get(sender, {})
+    if not profile:
+        raise Exception("Profile not found")
+
+    profile["age"] = new_age
+    storage[sender] = profile  # Re-saving the whole dictionary
+
+# -----------------------------------------------------------------------------
+# Paradigm 2: Composite Keys
+# -----------------------------------------------------------------------------
+# We namespace the keys using a string prefix (e.g., "age:0x123").
+# Pros: We can update individual fields independently without fetching everything.
+# Cons: Data is slightly fragmented across the storage dictionary.
+
+elif payload.startswith('set_composite:'):
+    parts = payload.split(':')
+    if len(parts) != 3:
+        raise Exception("Invalid format. Use set_composite:<age>:<name>")
+
+    age = int(parts[1])
+    name = parts[2]
+
+    # Store each field independently using namespaced keys
+    storage[f"age:{sender}"] = age
+    storage[f"name:{sender}"] = name
+
+elif payload.startswith('update_age_composite:'):
+    parts = payload.split(':')
+    if len(parts) != 2:
+        raise Exception("Invalid format. Use update_age_composite:<new_age>")
+
+    new_age = int(parts[1])
+
+    # Notice the efficiency here: we only interact with the exact
+    # piece of data we want to change, without touching the name at all.
+    if f"age:{sender}" not in storage:
+        raise Exception("Profile not found")
+
+    storage[f"age:{sender}"] = new_age
+
+else:
+    raise Exception("Unknown command. Valid commands: set_grouped, update_age_grouped, set_composite, update_age_composite")