code: package it.unibz.inf.ontop.dbschema.impl;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.ImmutableSet;
  import it.unibz.inf.ontop.dbschema.*;
  import it.unibz.inf.ontop.utils.ImmutableCollectors;
  
  import java.util.Optional;
  import java.util.stream.Collectors;
  
  public class UniqueConstraintImpl implements UniqueConstraint {
  
      private static class UniqueConstraintBuilder implements Builder {
          protected final ImmutableList.Builder<Attribute> builder = ImmutableList.builder();
          protected final NamedRelationDefinition relation;
          protected final String name;
  
          private UniqueConstraintBuilder(NamedRelationDefinition relation, String name) {
              this.relation = relation;
              this.name = name;
          }
  
          @Override
          public Builder addDeterminant(int determinantIndex) {
              builder.add(relation.getAttribute(determinantIndex));
              return this;
          }
  
          @Override
          public Builder addDeterminant(QuotedID determinantId) throws AttributeNotFoundException {
              builder.add(relation.getAttribute(determinantId));
              return this;
          }
  
          @Override
          public Builder addDependent(int dependentIndex) {
              throw new IllegalArgumentException("No dependents");
          }
  
          @Override
          public Builder addDependent(QuotedID dependentId) {
              throw new IllegalArgumentException("No dependents");
          }
  
          @Override
          public void build() {
              ImmutableList<Attribute> attributes = builder.build();
              if (attributes.isEmpty())
                  throw new IllegalArgumentException("UC cannot have no attributes");
  
              Optional<UniqueConstraint> pk = relation.getPrimaryKey();
              if (pk.isPresent() && pk.get().getAttributes().equals(attributes))
                  return; // ignore a unique constraint with the same attributes as the primary key
  
              relation.addFunctionalDependency(new UniqueConstraintImpl(name, false, attributes));
          }
      }
  
      private static class PrimaryKeyBuilder extends UniqueConstraintBuilder {
  
          private PrimaryKeyBuilder(NamedRelationDefinition relation, String name) {
              super(relation, name);
          }
  
          @Override
          public Builder addDeterminant(int determinantIndex) {
              Attribute attribute = relation.getAttribute(determinantIndex);
              if (attribute.isNullable())
                  throw new IllegalArgumentException("Nullable attribute " + attribute + " cannot be in a PK");
  
              builder.add(attribute);
              return this;
          }
  
          @Override
          public Builder addDeterminant(QuotedID determinantId) throws AttributeNotFoundException {
              Attribute attribute = relation.getAttribute(determinantId);
              if (attribute.isNullable())
                  throw new IllegalArgumentException("Nullable attribute " + attribute + " cannot be in a PK");
  
              builder.add(attribute);
              return this;
          }
  
          @Override
          public void build() {
              ImmutableList<Attribute> attributes = builder.build();
              if (attributes.isEmpty())
                  throw new IllegalArgumentException("PK cannot have no attributes");
  
              relation.addFunctionalDependency(new UniqueConstraintImpl(name, true, attributes));
          }
      }
  
      /**
       * creates a UNIQUE constraint builder
       *
       * @param relation
       * @param name
       * @return
       */
  
      public static Builder builder(NamedRelationDefinition relation, String name) {
          return new UniqueConstraintBuilder(relation, name);
      }
  
      /**
       * creates a PRIMARY KEY  builder
       *
       * @param relation
       * @param name
       * @return
       */
  
      public static Builder primaryKeyBuilder(NamedRelationDefinition relation, String name) {
          return new PrimaryKeyBuilder(relation, name);
      }
  
      private final String name;
      private final ImmutableList<Attribute> attributes;
      private final boolean isPrimaryKey;
  
      /**
       * private constructor (use Builder instead)
       *
       * @param name
       * @param attributes
       */
  
      private UniqueConstraintImpl(String name, boolean isPrimaryKey, ImmutableList<Attribute> attributes) {
          this.name = name;
          this.isPrimaryKey = isPrimaryKey;
          this.attributes = attributes;
      }
  
      /**
       * return the name of the constraint
       *
       * @return name
       */
  
      @Override
      public String getName() {
          return name;
      }
  
      /**
       * return true if it is a primary key and false otherwise
       *
       * @return true if it is a primary key constraint (false otherwise)
       */
  
      @Override
      public boolean isPrimaryKey() {
          return isPrimaryKey;
      }
  
      /**
       * return the list of attributes in the unique constraint
       *
       * @return list of attributes
       */
  
      @Override
      public ImmutableList<Attribute> getAttributes() {
          return attributes;
      }
  
      @Override
      public ImmutableSet<Attribute> getDeterminants() {
          return ImmutableSet.copyOf(attributes);
      }
  
      @Override
      public ImmutableSet<Attribute> getDependents() {
          return attributes.get(0).getRelation().getAttributes().stream()
                  .filter(a -> !attributes.contains(a))
                  .collect(ImmutableCollectors.toSet());
      }
  
      @Override
      public String toString() {
          return "ALTER TABLE " + ((NamedRelationDefinition)attributes.get(0).getRelation()).getID() +
                  " ADD CONSTRAINT " + name + (isPrimaryKey ? " PRIMARY KEY " : " UNIQUE ") +
                  "(" +
                  attributes.stream()
                          .map(Attribute::getID)
                          .map(QuotedID::toString)
                          .collect(Collectors.joining(", ")) +
                  ")";
      }
  
  }
  