Added primitive foreign key stuff.

src/main/java/nl/andrewlalis/erme/control/actions/edits/AddAttributeAction.java

@@ -1,10 +1,7 @@
 package nl.andrewlalis.erme.control.actions.edits;
 
 import lombok.Setter;
-import nl.andrewlalis.erme.model.Attribute;
+import nl.andrewlalis.erme.model.*;
-import nl.andrewlalis.erme.model.AttributeType;
-import nl.andrewlalis.erme.model.MappingModel;
-import nl.andrewlalis.erme.model.Relation;
 
 import javax.swing.*;
 import java.awt.*;
@@ -49,6 +46,7 @@ public class AddAttributeAction extends AbstractAction {
 		Relation r = selectedRelations.get(0);
 		Component c = (Component) e.getSource();
 		String name = JOptionPane.showInputDialog(c, "Enter the name of the attribute.", "Attribute Name", JOptionPane.PLAIN_MESSAGE);
+		if (name == null) return;
 		Integer index = (Integer) JOptionPane.showInputDialog(
 				c,
 				"Select the index to insert this attribute at.",
@@ -67,7 +65,38 @@ public class AddAttributeAction extends AbstractAction {
 				AttributeType.values(),
 				AttributeType.PLAIN
 		);
-		if (name != null && index != null && type != null) {
+		if (type.equals(AttributeType.FOREIGN_KEY)) {
+			if (this.model.getRelations().size() < 2) {
+				JOptionPane.showMessageDialog(c, "There should be at least 2 relations present in the model.", "Not Enough Relations", JOptionPane.WARNING_MESSAGE);
+				return;
+			}
+			Relation fkRelation = (Relation) JOptionPane.showInputDialog(
+					c,
+					"Select the relation that this foreign key references.",
+					"Foreign Key Relation Reference",
+					JOptionPane.PLAIN_MESSAGE,
+					null,
+					this.model.getRelations().toArray(new Relation[0]),
+					this.model.getRelations().stream().findFirst().orElse(null)
+			);
+			List<Attribute> eligibleAttributes = fkRelation.getReferencableAttributes();
+			if (eligibleAttributes.isEmpty()) {
+				JOptionPane.showMessageDialog(c, "There are no referencable attributes in the selected relation.", "No Referencable Attributes", JOptionPane.WARNING_MESSAGE);
+				return;
+			}
+			Attribute fkAttribute = (Attribute) JOptionPane.showInputDialog(
+					c,
+					"Select the attribute that this foreign key references.",
+					"Foreign Key Attribute Reference",
+					JOptionPane.PLAIN_MESSAGE,
+					null,
+					eligibleAttributes.toArray(new Attribute[0]),
+					eligibleAttributes.get(0)
+			);
+			if (fkAttribute != null) {
+				r.addAttribute(new ForeignKeyAttribute(r, name, fkAttribute));
+			}
+		} else {
 			r.addAttribute(new Attribute(r, type, name), index);
 		}
 	}

src/main/java/nl/andrewlalis/erme/model/Attribute.java

@@ -1,6 +1,7 @@
 package nl.andrewlalis.erme.model;
 
 import lombok.Getter;
+import nl.andrewlalis.erme.view.view_models.AttributeViewModel;
 
 import java.io.Serializable;
 import java.util.Objects;
@@ -14,6 +15,8 @@ public class Attribute implements Serializable {
 	private AttributeType type;
 	private String name;
 
+	private AttributeViewModel viewModel;
+
 	public Attribute(Relation relation, AttributeType type, String name) {
 		this.relation = relation;
 		this.type = type;
@@ -30,6 +33,13 @@ public class Attribute implements Serializable {
 		this.relation.getModel().fireChangedEvent();
 	}
 
+	public AttributeViewModel getViewModel() {
+		if (this.viewModel == null) {
+			this.viewModel = new AttributeViewModel(this);
+		}
+		return this.viewModel;
+	}
+
 	@Override
 	public boolean equals(Object o) {
 		if (this == o) return true;

src/main/java/nl/andrewlalis/erme/model/ForeignKeyAttribute.java

@@ -0,0 +1,25 @@
+package nl.andrewlalis.erme.model;
+
+import lombok.Getter;
+
+@Getter
+public class ForeignKeyAttribute extends Attribute {
+	private Attribute reference;
+
+	public ForeignKeyAttribute(Relation relation, String name, Attribute reference) {
+		super(relation, AttributeType.FOREIGN_KEY, name);
+		this.reference = reference;
+	}
+
+	public ForeignKeyAttribute(Relation relation, String name, String referencedRelationName, String referencedAttributeName) {
+		this(relation, name, relation.getModel().findAttribute(referencedRelationName, referencedAttributeName));
+		if (this.getReference() == null) {
+			throw new IllegalArgumentException("Unknown attribute name.");
+		}
+	}
+
+	public void setReference(Attribute reference) {
+		this.reference = reference;
+		this.getRelation().getModel().fireChangedEvent();
+	}
+}

src/main/java/nl/andrewlalis/erme/model/MappingModel.java

@@ -40,6 +40,18 @@ public class MappingModel implements Serializable {
 		return this.relations.stream().filter(Relation::isSelected).collect(Collectors.toList());
 	}
 
+	public Attribute findAttribute(String relationName, String attributeName) {
+		for (Relation r : this.getRelations()) {
+			if (!r.getName().equals(relationName)) continue;
+			for (Attribute a : r.getAttributes()) {
+				if (a.getName().equals(attributeName)) {
+					return a;
+				}
+			}
+		}
+		return null;
+	}
+
 	public void addChangeListener(ModelChangeListener listener) {
 		if (this.changeListeners == null) {
 			this.changeListeners = new HashSet<>();

src/main/java/nl/andrewlalis/erme/model/Relation.java

@@ -8,6 +8,7 @@ import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
+import java.util.stream.Collectors;
 
 /**
  * Represents a single "relation" or table in the diagram.
@@ -64,6 +65,12 @@ public class Relation implements Serializable {
 		return this.viewModel;
 	}
 
+	public List<Attribute> getReferencableAttributes() {
+		return this.attributes.stream()
+				.filter(a -> a.getType() == AttributeType.ID_KEY || a.getType() == AttributeType.PARTIAL_ID_KEY)
+				.collect(Collectors.toList());
+	}
+
 	@Override
 	public boolean equals(Object o) {
 		if (this == o) return true;

src/main/java/nl/andrewlalis/erme/view/EditorFrame.java

@@ -1,9 +1,6 @@
 package nl.andrewlalis.erme.view;
 
-import nl.andrewlalis.erme.model.Attribute;
+import nl.andrewlalis.erme.model.*;
-import nl.andrewlalis.erme.model.AttributeType;
-import nl.andrewlalis.erme.model.MappingModel;
-import nl.andrewlalis.erme.model.Relation;
 
 import javax.swing.*;
 import java.awt.*;
@@ -24,7 +21,7 @@ public class EditorFrame extends JFrame {
 		model.addRelation(usersRelation);
 		Relation tokensRelation = new Relation(model, new Point(50, 120), "Tokens");
 		tokensRelation.addAttribute(new Attribute(tokensRelation, AttributeType.ID_KEY, "tokenCode"));
-		tokensRelation.addAttribute(new Attribute(tokensRelation, AttributeType.FOREIGN_KEY, "username"));
+		tokensRelation.addAttribute(new ForeignKeyAttribute(tokensRelation,"username", "Users", "username"));
 		tokensRelation.addAttribute(new Attribute(tokensRelation, AttributeType.PLAIN, "expirationDate"));
 		model.addRelation(tokensRelation);
 

src/main/java/nl/andrewlalis/erme/view/view_models/RelationViewModel.java

@@ -25,7 +25,7 @@ public class RelationViewModel implements ViewModel {
 		g.setColor(Color.BLACK);
 		g.drawString(as.getIterator(), bounds.x + PADDING_X, bounds.y + this.getNameBounds(g).height - PADDING_Y);
 		for (Attribute a : this.relation.getAttributes()) {
-			new AttributeViewModel(a).draw(g);
+			a.getViewModel().draw(g);
 		}
 		if (this.relation.isSelected()) {
 			g.setColor(Color.BLUE);
@@ -40,7 +40,7 @@ public class RelationViewModel implements ViewModel {
 		int totalAttributeWidth = 0;
 		int maxAttributeHeight = 0;
 		for (Attribute a : this.relation.getAttributes()) {
-			Rectangle attributeBounds = new AttributeViewModel(a).getBounds(g);
+			Rectangle attributeBounds = a.getViewModel().getBounds(g);
 			totalAttributeWidth += attributeBounds.width;
 			maxAttributeHeight = Math.max(maxAttributeHeight, attributeBounds.height);
 		}