👌 IMPROVE: Add solution for validation exercise

docs/sections/writing_workflows/include/code/validation/validated_multiple_add.py

@@ -0,0 +1,66 @@
+from aiida.orm import Int, Float
+from aiida.engine import WorkChain, calcfunction
+
+
+@calcfunction
+def addition(x, y):
+    return x + y
+
+
+@calcfunction
+def multiplication(x, y):
+    return x * y
+
+
+def validate_z(node, _):
+    """Validate the `z` input."""
+    if node.value == 0:
+        return "The value of `z` can not be zero."
+
+
+def validate_inputs(inputs, _):
+    """Validate the top-level inputs."""
+    if inputs["x"] + inputs["y"] == 0:
+        return "The sum of `x` and `y` can not be zero."
+
+
+class MultiplyAddWorkChain(WorkChain):
+    """WorkChain to multiply two integers and add a third."""
+
+    @classmethod
+    def define(cls, spec):
+        """Specify inputs, outputs, and the workchain outline."""
+        super().define(spec)
+
+        spec.input("x", valid_type=(Int, Float))
+        spec.input("y", valid_type=(Int, Float))
+        spec.input("z", valid_type=Int, validator=validate_z)
+        spec.inputs.validator = validate_inputs
+
+        spec.outline(cls.multiply, cls.add, cls.result)
+        spec.output("workchain_result", valid_type=(Int, Float))
+        spec.output("product", valid_type=(Int, Float))
+
+    def multiply(self):
+        """Multiply two integers."""
+
+        multiplication_result = multiplication(self.inputs.x, self.inputs.y)
+
+        # Passing to context to be used by other functions
+        self.ctx.product = multiplication_result
+
+    def add(self):
+        """Add two numbers."""
+
+        # Call `addition` using a variable from the context and one of the inputs
+        addition_result = addition(self.ctx.product, self.inputs.z)
+
+        # Passing to context to be used by other functions
+        self.ctx.summation = addition_result
+
+    def result(self):
+        """Parse the result."""
+
+        # Declaring the output
+        self.out("workchain_result", self.ctx.summation)
+        self.out("product", self.ctx.product)

docs/sections/writing_workflows/validation.md

@@ -151,3 +151,14 @@ Take the `MultiplyAddWorkChain` from the {ref}`exercise in the work chains secti
 * Allow the `x` and `y` inputs to _also_ be `Float` nodes.
 * Make sure `z` is not zero.
 * Make sure the sum of `x` and `y` is not zero.
+
+:::{dropdown} **Solution**
+
+```{literalinclude} include/code/validation/validated_multiple_add.py
+:language: python
+:emphasize-lines: 14-17, 19-22, 32-35, 38-39
+```
+
+Note how the `valid_type` of the _outputs_ also has to be more flexible!
+
+:::