package org.mongodb.morphia.query.validation;

import org.mongodb.morphia.mapping.MappedField;
import org.mongodb.morphia.query.FilterOperator;

import java.util.List;

import static java.lang.String.format;
import static org.mongodb.morphia.query.FilterOperator.EXISTS;

Checks if the value can have the FilterOperator.EXISTS operator applied to it. Since this class does not need state, and the methods can't be static because it implements an interface, it seems to be one of the few places where the Singleton pattern seems appropriate. /**
 * Checks if the value can have the {@code FilterOperator.EXISTS} operator applied to it.  Since this class does not need state, and the
 * methods can't be static because it implements an interface, it seems to be one of the few places where the Singleton pattern seems
 * appropriate.
 */
public final class ExistsOperationValidator extends OperationValidator {
    private static final ExistsOperationValidator INSTANCE = new ExistsOperationValidator();

    private ExistsOperationValidator() {
    }

    
Get the instance.
Returns:
the Singleton instance of this validator/**
     * Get the instance.
     *
     * @return the Singleton instance of this validator
     */
    public static ExistsOperationValidator getInstance() {
        return INSTANCE;
    }

    @Override
    protected FilterOperator getOperator() {
        return EXISTS;
    }

    @Override
    protected void validate(final MappedField mappedField, final Object value, final List<ValidationFailure> validationFailures) {
        if (value.getClass() != Boolean.class) {
            validationFailures.add(new ValidationFailure(format("For an $exists operation, value '%s' should be a boolean type.  "
                                                                + "Instead it was a: %s", value, value.getClass())));
        }
    }
}