Added better mouse functionality and save.

src/main/java/nl/andrewlalis/erme/control/actions/SaveAction.java

@@ -0,0 +1,63 @@
+package nl.andrewlalis.erme.control.actions;
+
+import lombok.Setter;
+import nl.andrewlalis.erme.model.MappingModel;
+
+import javax.swing.*;
+import javax.swing.filechooser.FileNameExtensionFilter;
+import java.awt.*;
+import java.awt.event.ActionEvent;
+import java.awt.event.InputEvent;
+import java.awt.event.KeyEvent;
+import java.io.*;
+
+public class SaveAction extends AbstractAction {
+	private static SaveAction instance;
+
+	public static SaveAction getInstance() {
+		if (instance == null) {
+			instance = new SaveAction();
+		}
+		return instance;
+	}
+
+	private File lastSelectedFile;
+
+	@Setter
+	private MappingModel model;
+
+	public SaveAction() {
+		super("Save");
+		this.putValue(SHORT_DESCRIPTION, "Save the current diagram to a file.");
+		this.putValue(ACCELERATOR_KEY, KeyStroke.getKeyStroke(KeyEvent.VK_S, InputEvent.CTRL_DOWN_MASK));
+	}
+
+	@Override
+	public void actionPerformed(ActionEvent e) {
+		JFileChooser fileChooser = new JFileChooser(this.lastSelectedFile);
+		FileNameExtensionFilter filter = new FileNameExtensionFilter(
+				"ERME Serialized Files",
+				"erme"
+		);
+		fileChooser.setFileFilter(filter);
+		int choice = fileChooser.showSaveDialog((Component) e.getSource());
+		if (choice == JFileChooser.APPROVE_OPTION) {
+			File chosenFile = fileChooser.getSelectedFile();
+			if (chosenFile == null || chosenFile.isDirectory()) {
+				JOptionPane.showMessageDialog(fileChooser, "The selected file cannot be written to.", "Invalid File", JOptionPane.WARNING_MESSAGE);
+				return;
+			}
+			if (!chosenFile.exists() && !chosenFile.getName().endsWith(".erme")) {
+				chosenFile = new File(chosenFile.getParent(), chosenFile.getName() + ".erme");
+			}
+			// TODO: Check for confirm before overwriting.
+			try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(chosenFile))) {
+				oos.writeObject(this.model);
+				this.lastSelectedFile = chosenFile;
+				JOptionPane.showMessageDialog(fileChooser, "File saved successfully.", "Success", JOptionPane.INFORMATION_MESSAGE);
+			} catch (IOException ex) {
+				JOptionPane.showMessageDialog(fileChooser, "An error occurred and the file could not be saved:\n" + ex.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
+			}
+		}
+	}
+}

src/main/java/nl/andrewlalis/erme/control/diagram/DiagramMouseListener.java

@@ -18,23 +18,32 @@ public class DiagramMouseListener extends MouseAdapter {
 		this.model = model;
 	}
 
+	/**
+	 * Handles mouse presses. This is what should happen:
+	 * - If the click occurs outside of the bounds of any relation, deselect all
+	 * relations, if CTRL is not held down.
+	 * - If the click occurs within at least one relation, select the first one,
+	 * and deselect all others if CTRL is not held down.
+	 * @param e The mouse event.
+	 */
 	@Override
 	public void mousePressed(MouseEvent e) {
 		DiagramPanel panel = (DiagramPanel) e.getSource();
 		final Graphics2D g2d = panel.getGraphics2D();
 		this.mouseDragStart = e.getPoint();
-		if ((e.getModifiers() & ActionEvent.CTRL_MASK) == ActionEvent.CTRL_MASK) {
-			boolean hit = false;
-			for (Relation r : this.model.getRelations()) {
-				if (r.getViewModel().getBounds(g2d).contains(e.getX(), e.getY())) {
-					r.setSelected(!r.isSelected());
-					hit = true;
-				}
-			}
-			if (!hit) {
-				this.model.getRelations().forEach(r -> r.setSelected(false));
+
+		boolean isCtrlDown = (e.getModifiers() & ActionEvent.CTRL_MASK) == ActionEvent.CTRL_MASK;
+
+		if (!isCtrlDown) {
+			this.model.getRelations().forEach(r -> r.setSelected(false));
+		}
+		for (Relation r : this.model.getRelations()) {
+			if (r.getViewModel().getBounds(g2d).contains(e.getX(), e.getY())) {
+				r.setSelected(!r.isSelected());
+				break;
 			}
 		}
+		this.model.fireChangedEvent();
 	}
 
 	@Override
@@ -46,11 +55,16 @@ public class DiagramMouseListener extends MouseAdapter {
 	public void mouseDragged(MouseEvent e) {
 		int dx = this.mouseDragStart.x - e.getX();
 		int dy = this.mouseDragStart.y - e.getY();
+		boolean changed = false;
 		for (Relation r : this.model.getRelations()) {
 			if (r.isSelected()) {
 				r.setPosition(new Point(r.getPosition().x - dx, r.getPosition().y - dy));
+				changed = true;
 			}
 		}
+		if (changed) {
+			this.model.fireChangedEvent();
+		}
 		this.mouseDragStart = e.getPoint();
 	}
 

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

@@ -2,13 +2,14 @@ package nl.andrewlalis.erme.model;
 
 import lombok.Getter;
 
+import java.io.Serializable;
 import java.util.Objects;
 
 /**
  * A single value that belongs to a relation.
  */
 @Getter
-public class Attribute {
+public class Attribute implements Serializable {
 	private final Relation relation;
 	private AttributeType type;
 	private String name;

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

@@ -2,6 +2,7 @@ package nl.andrewlalis.erme.model;
 
 import lombok.Getter;
 
+import java.io.Serializable;
 import java.util.HashSet;
 import java.util.Objects;
 import java.util.Set;
@@ -10,11 +11,11 @@ import java.util.Set;
  * This model contains all the information about a single mapping diagram,
  * including each mapped table and the links between them.
  */
-public class MappingModel {
+public class MappingModel implements Serializable {
 	@Getter
 	private final Set<Relation> relations;
 
-	private final Set<ModelChangeListener> changeListeners;
+	private transient final Set<ModelChangeListener> changeListeners;
 
 	public MappingModel() {
 		this.relations = new HashSet<>();
@@ -38,7 +39,7 @@ public class MappingModel {
 		listener.onModelChanged();
 	}
 
-	protected final void fireChangedEvent() {
+	public final void fireChangedEvent() {
 		this.changeListeners.forEach(ModelChangeListener::onModelChanged);
 	}
 

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

@@ -4,6 +4,7 @@ import lombok.Getter;
 import nl.andrewlalis.erme.view.view_models.RelationViewModel;
 
 import java.awt.*;
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
@@ -12,7 +13,7 @@ import java.util.Objects;
  * Represents a single "relation" or table in the diagram.
  */
 @Getter
-public class Relation {
+public class Relation implements Serializable {
 	private final MappingModel model;
 	private Point position;
 	private String name;
@@ -30,24 +31,15 @@ public class Relation {
 	}
 
 	public void setPosition(Point position) {
-		if (!this.position.equals(position)) {
-			this.position = position;
-			this.model.fireChangedEvent();
-		}
+		this.position = position;
 	}
 
 	public void setName(String name) {
-		if (!this.name.equals(name)) {
-			this.name = name;
-			this.model.fireChangedEvent();
-		}
+		this.name = name;
 	}
 
 	public void setSelected(boolean selected) {
-		if (selected != this.selected) {
-			this.selected = selected;
-			this.model.fireChangedEvent();
-		}
+		this.selected = selected;
 	}
 
 	public void addAttribute(Attribute attribute) {

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

@@ -1,6 +1,7 @@
 package nl.andrewlalis.erme.view;
 
 import lombok.Getter;
+import nl.andrewlalis.erme.control.actions.SaveAction;
 import nl.andrewlalis.erme.control.diagram.DiagramMouseListener;
 import nl.andrewlalis.erme.model.MappingModel;
 import nl.andrewlalis.erme.model.ModelChangeListener;
@@ -35,6 +36,7 @@ public class DiagramPanel extends JPanel implements ModelChangeListener {
 		DiagramMouseListener listener = new DiagramMouseListener(newModel);
 		this.addMouseListener(listener);
 		this.addMouseMotionListener(listener);
+		SaveAction.getInstance().setModel(newModel);
 		this.repaint();
 	}
 

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

@@ -1,9 +1,6 @@
 package nl.andrewlalis.erme.view;
 
-import nl.andrewlalis.erme.control.actions.ExitAction;
-import nl.andrewlalis.erme.control.actions.ExportToImageAction;
-import nl.andrewlalis.erme.control.actions.RedoAction;
-import nl.andrewlalis.erme.control.actions.UndoAction;
+import nl.andrewlalis.erme.control.actions.*;
 
 import javax.swing.*;
 
@@ -18,6 +15,8 @@ public class EditorMenuBar extends JMenuBar {
 
 	private JMenu buildFileMenu() {
 		JMenu menu = new JMenu("File");
+		JMenuItem saveItem = new JMenuItem(SaveAction.getInstance());
+		menu.add(saveItem);
 		JMenuItem exportAsImageItem = new JMenuItem(ExportToImageAction.getInstance());
 		menu.add(exportAsImageItem);
 		JMenuItem exitItem = new JMenuItem(ExitAction.getInstance());

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

@@ -29,10 +29,8 @@ public class RelationViewModel implements ViewModel {
 		}
 		if (this.relation.isSelected()) {
 			g.setColor(Color.BLUE);
-		} else {
-			g.setColor(Color.CYAN);
+			g.drawRect(bounds.x, bounds.y, bounds.width, bounds.height);
 		}
-		g.drawRect(bounds.x, bounds.y, bounds.width, bounds.height);
 	}
 
 	public Rectangle getBounds(Graphics2D g) {