HHH-19614 generate CHECK constraint to enforce non-nullability in SINGLE_TABLE inheritance

hibernate-core/src/main/java/org/hibernate/boot/model/internal/EntityBinder.java

@@ -219,6 +219,9 @@ public static void bindEntityClass(
 			assert superEntity != null;
 			superEntity.addSubclass( subclass );
 		}
+
+		persistentClass.createConstraints( context );
+
 		collector.addEntityBinding( persistentClass );
 		// process secondary tables and complementary definitions (ie o.h.a.Table)
 		collector.addSecondPass( new SecondaryTableFromAnnotationSecondPass( entityBinder, holder ) );

hibernate-core/src/main/java/org/hibernate/mapping/Column.java

@@ -16,6 +16,7 @@
 import org.hibernate.boot.Metadata;
 import org.hibernate.boot.model.naming.Identifier;
 import org.hibernate.boot.model.relational.Database;
+import org.hibernate.boot.spi.InFlightMetadataCollector;
 import org.hibernate.boot.spi.MetadataBuildingContext;
 import org.hibernate.dialect.Dialect;
 import org.hibernate.engine.jdbc.Size;
@@ -117,7 +118,11 @@ public void setValue(Value value) {
 	}
 
 	public JdbcMapping getType() {
-		return getValue().getSelectableType( getValue().getBuildingContext().getMetadataCollector(), getTypeIndex() );
+		return getValue().getSelectableType( getMetadataCollector(), getTypeIndex() );
+	}
+
+	private InFlightMetadataCollector getMetadataCollector() {
+		return getValue().getBuildingContext().getMetadataCollector();
 	}
 
 	public String getName() {
@@ -176,22 +181,16 @@ private static boolean isCloseQuote(char ch) {
 	 * @return the quoted name as it would occur in the mapping file
 	 */
 	public String getQuotedName() {
-		return safeInterning(
-				quoted ?
-				"`" + name + "`" :
-				name
-		);
+		return safeInterning( quoted ? "`" + name + "`" : name );
 	}
 
 	/**
 	 * @return the quoted name using the quoting syntax of the given dialect
 	 */
 	public String getQuotedName(Dialect dialect) {
-		return safeInterning(
-				quoted ?
-				dialect.openQuote() + name + dialect.closeQuote() :
-				name
-		);
+		return safeInterning( quoted
+				? dialect.openQuote() + name + dialect.closeQuote()
+				: name );
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/mapping/PersistentClass.java

@@ -1230,4 +1230,7 @@ public void removeProperty(Property property) {
 		}
 		properties.remove( property );
 	}
+
+	public void createConstraints(MetadataBuildingContext context) {
+	}
 }

hibernate-core/src/main/java/org/hibernate/mapping/Property.java

@@ -496,7 +496,10 @@ public Generator createGenerator(RuntimeModelCreationContext context) {
 	}
 
 	public Property copy() {
-		final Property property = this instanceof SyntheticProperty ? new SyntheticProperty() : new Property();
+		final Property property =
+				this instanceof SyntheticProperty
+						? new SyntheticProperty()
+						: new Property();
 		property.setName( getName() );
 		property.setValue( getValue() );
 		property.setCascade( getCascade() );

hibernate-core/src/main/java/org/hibernate/mapping/SingleTableSubclass.java

@@ -9,8 +9,12 @@
 import org.hibernate.MappingException;
 import org.hibernate.boot.Metadata;
 import org.hibernate.boot.spi.MetadataBuildingContext;
+import org.hibernate.dialect.Dialect;
 import org.hibernate.internal.util.collections.JoinedList;
 
+import static org.hibernate.persister.entity.DiscriminatorHelper.getDiscriminatorSQLValue;
+
+
 /**
  * A mapping model object that represents a subclass in a
  * {@linkplain jakarta.persistence.InheritanceType#SINGLE_TABLE single table}
@@ -40,4 +44,55 @@ public void validate(Metadata mapping) throws MappingException {
 		}
 		super.validate( mapping );
 	}
+
+	@Override
+	public void createConstraints(MetadataBuildingContext context) {
+		if ( !isAbstract() ) {
+			final Dialect dialect = context.getMetadataCollector().getDatabase().getDialect();
+			if ( dialect.supportsTableCheck() ) {
+				final Value discriminator = getDiscriminator();
+				final List<Selectable> selectables = discriminator.getSelectables();
+				if ( selectables.size() == 1 ) {
+					final StringBuilder check = new StringBuilder();
+					check.append( selectables.get( 0 ).getText( dialect ) );
+					if ( isDiscriminatorValueNull() ) {
+						check.append( " is " );
+					}
+					else if ( isDiscriminatorValueNotNull() ) {
+						check.append( " is " );
+						// can't enforce this for now, because 'not null'
+						// really means "not null and not any of the other
+						// explicitly listed values"
+						return;  //ABORT
+					}
+					else {
+						check.append( " <> " );
+					}
+					check.append( getDiscriminatorSQLValue( this, dialect ) )
+							.append( " or (" );
+					boolean first = true;
+					for ( Property property : getNonDuplicatedProperties() ) {
+						if ( !property.isComposite() && !property.isOptional() ) {
+							for ( Selectable selectable : property.getSelectables() ) {
+								if ( selectable instanceof Column column && column.isNullable() ) {
+									if ( first ) {
+										first = false;
+									}
+									else {
+										check.append( " and " );
+									}
+									check.append( column.getQuotedName( dialect ) )
+											.append( " is not null" );
+								}
+							}
+						}
+					}
+					check.append( ")" );
+					if ( !first ) {
+						getTable().addCheck( new CheckConstraint( check.toString() ) );
+					}
+				}
+			}
+		}
+	}
 }