Vaadin Web应用开发教程(49): SQLContainer-引用其它SQLContainer

数据库表之间存在参考关键，这对应到数据库通常为外键引用。Vaadin 的SQLContainer提供了不同SQLContainer之间引用的有限支持，但其实现主要是通过Java 代码来实现的，并不需要数据库的表之间一定要有外键定义。

给一个SQLContainer添加引用的方法为：

[java]
public void addReference(SQLContainer refdCont,
String refingCol, String refdCol);

public void addReference(SQLContainer refdCont,
String refingCol, String refdCol);

refdCont为被引用的SQLContainer，refingCol 为源SQLContainer对应的列名，refdCol为目标SQLContainer被参照的列名。
要注意的是SQLContainer不支持同一个SQLContainer参照自身。

还是以Customer ,Invoice 为例。显示所有Invoice，但点击某个Invoice，显示对应的Customer的姓名。

[java]
void openTable(VerticalLayout layout){
    try {
        JDBCConnectionPool pool = new SimpleJDBCConnectionPool(
                "org.hsqldb.jdbc.JDBCDriver",
                "jdbc:hsqldb:file:/hsqldb/data/sample", "SA", "", 2, 5);
        TableQuery customers = new TableQuery("CUSTOMER", pool);
        customers.setVersionColumn("OPTLOCK");
        TableQuery invoices = new TableQuery("INVOICE", pool);
        customers.setVersionColumn("OPTLOCK");
        final SQLContainer customerContainer
                        = new SQLContainer(customers);
        final SQLContainer invoiceContainer
                       = new SQLContainer(invoices);
        Table table = new Table("All Invoices", invoiceContainer);
        table.setSelectable(true);

        // Send changes in selection immediately to server.
        table.setImmediate(true);

        invoiceContainer.addReference(customerContainer,
                           "CUSTOMERID", "ID");

        table.addListener(new ItemClickListener(){

            public void itemClick(ItemClickEvent event) {
                RowItem rowItem=(RowItem)event.getItem();

                RowItem customerItem
                    =(RowItem)invoiceContainer
                    .getReferencedItem(rowItem.getId(),
                            customerContainer);

                customerLabel.setValue(customerItem
                               .getItemProperty("FIRSTNAME")
                               .toString()
                                +" "+ customerItem
                                .getItemProperty("LASTNAME")
                                .toString());

            }});
        layout.addComponent(table);

    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

void openTable(VerticalLayout layout){
try {
  JDBCConnectionPool pool = new SimpleJDBCConnectionPool(
    "org.hsqldb.jdbc.JDBCDriver",
    "jdbc:hsqldb:file:/hsqldb/data/sample", "SA", "", 2, 5);
  TableQuery customers = new TableQuery("CUSTOMER", pool);
  customers.setVersionColumn("OPTLOCK");
  TableQuery invoices = new TableQuery("INVOICE", pool);
  customers.setVersionColumn("OPTLOCK");
  final SQLContainer customerContainer
                        = new SQLContainer(customers);
  final SQLContainer invoiceContainer
                       = new SQLContainer(invoices);
  Table table = new Table("All Invoices", invoiceContainer);
  table.setSelectable(true);

// Send changes in selection immediately to server.
table.setImmediate(true);

invoiceContainer.addReference(customerContainer,
&nbs

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