# Body - Fields

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field`

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

	if f.Ref == nil {
		f.Ref = make([]*Ref, 0, 8)
	}
	f.walk(ast2, ctxProg, (*File).validateIdents)
	f.walk(ast2, ctxProg, (*File).saveExprs)

	// Accumulate exported functions.
	// The comments are only on ast1 but we need to
	// save the function bodies from ast2.
	// The first walk fills in ExpFunc, and the
	// second walk changes the entries to
	// refer to ast2 instead.
	f.walk(ast1, ctxProg, (*File).saveExport)

import com.google.common.annotations.GwtCompatible;
import java.util.Arrays;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Helper functions that can operate on any {@code Object}.
 *
 * <p>See the Guava User Guide on <a
 * href="https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained">writing {@code Object}
 * methods with {@code Objects}</a>.
 *

			return nil
		}
		return apiErr
	}
	return nil
}

// GetObjectLambdaHandler - GET Object with transformed data via lambda functions
// ----------
// This implementation of the GET operation applies lambda functions and returns the
// response generated via the lambda functions. To use this API, you must have READ access
// to the object.

import com.google.common.annotations.GwtCompatible;
import java.util.Arrays;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Helper functions that can operate on any {@code Object}.
 *
 * <p>See the Guava User Guide on <a
 * href="https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained">writing {@code Object}
 * methods with {@code Objects}</a>.
 *

// TFE_Execute by creating an op with the same name as the function.
TF_CAPI_EXPORT extern void TFE_ContextAddFunction(TFE_Context* ctx,
                                                  TF_Function* function,
                                                  TF_Status* status);

// Removes a function from the context. Once removed, you can no longer
// TFE_Execute it or TFE_Execute any TFE_Op which has it as an attribute or any

   * {@code function} to the argument, then evaluating using {@code this}. That is, for any pair of
   * non-null objects {@code x} and {@code y}, {@code equivalence.onResultOf(function).equivalent(a,
   * b)} is true if and only if {@code equivalence.equivalent(function.apply(a), function.apply(b))}
   * is true.
   *
   * <p>For example:
   *
   * <pre>{@code

# ==============================================================================
#
# Common setup for all TF scripts.
#
# Make as FEW changes to this file as possible. It should not contain utility
# functions (except for tfrun); use dedicated scripts instead and reference them
# specifically. Use your best judgment to keep the scripts in this directory
# lean and easy to follow. When in doubt, remember that for CI scripts, "keep it

## Return Type and Data Filtering

Let's continue from the previous example. We wanted to **annotate the function with one type**, but we wanted to be able to return from the function something that actually includes **more data**.

We want FastAPI to keep **filtering** the data using the response model. So that even though the function returns more data, the response will only include the fields declared in the response model.

// current row and stores the result.
//
// On success, it returns (nil, nil).
func (e *FuncExpr) evalAggregationNode(r Record, tableAlias string) error {
	// It is assumed that this function is called only when
	// `e` is an aggregation function.

	var val *Value
	var err error
	funcName := e.getFunctionName()
	if aggFnCount == funcName {
		if e.Count.StarArg {
			// Handle COUNT(*)
			e.aggregate.runningCount++