# Extending OpenAPI

There are some cases where you might need to modify the generated OpenAPI schema.

In this section you will see how.

## The normal process

The normal (default) process, is as follows.

A `FastAPI` application (instance) has an `.openapi()` method that is expected to return the OpenAPI schema.

  // For example: (long) data[i++] | (long) data[i++] << 8 | ...
  // If data[i] == (byte) 0x80, the first cast will sign-extend it to 0xffffffffffffff80,
  // masking the remaining seven bytes.
  // To test this, we give an input where bit 7 is not cleared. For example:
  // (1) 00 01 02 03 04 05 06 07 80
  // (2) 00 01 02 03 04 05 06 07 81
  // (3) 00 01 02 03 04 05 06 07 ff (or anything in between)

  // For example: (long) data[i++] | (long) data[i++] << 8 | ...
  // If data[i] == (byte) 0x80, the first cast will sign-extend it to 0xffffffffffffff80,
  // masking the remaining seven bytes.
  // To test this, we give an input where bit 7 is not cleared. For example:
  // (1) 00 01 02 03 04 05 06 07 80
  // (2) 00 01 02 03 04 05 06 07 81
  // (3) 00 01 02 03 04 05 06 07 ff (or anything in between)

        return locations != null ? locations.get(key) : null;
    }

    public Map<Object, InputLocation> getLocations() {
        return locations;
    }

    /**
     * Gets the parent InputLocation where this InputLocation may have been imported from.
     * Can return {@code null}.
     *
     * @return InputLocation
     * @since 4.0.0
     */
    public InputLocation getImportedFrom() {

    public ModelBuildingException(ModelBuildingResult result) {
        super(toMessage(result));
        this.result = result;
    }

    /**
     * Gets the interim result of the model building up to the point where it failed.
     *
     * @return The interim model building result or {@code null} if not available.
     */
    public ModelBuildingResult getResult() {
        return result;
    }

    /**

	if !found {
		return nil, &ErrARNNotFound{}
	}
	return id, nil
}

// TargetIDResult returns result of Remove/Send operation, sets err if
// any for the associated TargetID
type TargetIDResult struct {
	// ID where the remove or send were initiated.
	ID TargetID
	// Stores any error while removing a target or while sending an event.
	Err error
}

// Remove - closes and removes targets by given target IDs.

   *
   * @see java.util.Collection the definition of general-purpose collections.
   */
  GENERAL_PURPOSE(SUPPORTS_ADD, SUPPORTS_REMOVE, SUPPORTS_ITERATOR_REMOVE),

  /** Features supported by collections where only removal is allowed. */
  REMOVE_OPERATIONS(SUPPORTS_REMOVE, SUPPORTS_ITERATOR_REMOVE),

  SERIALIZABLE,
  SERIALIZABLE_INCLUDING_VIEWS(SERIALIZABLE),

  SUBSET_VIEW,
  DESCENDING_VIEW,

  /**

import java.util.List;

/**
 * Tester for {@link Equivalence} relationships between groups of objects.
 *
 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
 * contains objects that are supposed to be equal to each other. Objects of different groups are
 * expected to be unequal. For example:
 *
 * <pre>{@code
 * EquivalenceTester.of(someStringEquivalence)

import java.util.List;

/**
 * Tester for {@link Equivalence} relationships between groups of objects.
 *
 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
 * contains objects that are supposed to be equal to each other. Objects of different groups are
 * expected to be unequal. For example:
 *
 * <pre>{@code
 * EquivalenceTester.of(someStringEquivalence)

 * @since 2.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingSet<E extends @Nullable Object> extends ForwardingCollection<E>
    implements Set<E> {
  // TODO(lowasser): identify places where thread safety is actually lost

  /** Constructor for use by subclasses. */
  protected ForwardingSet() {}

  @Override
  protected abstract Set<E> delegate();

  @Override