java - COALESCE SQL 与 Speedment

Question

评估可能参数的 Hibernate 代码示例:

  String query = "SELECT * FROM instances";
  String where = "";
  if(userName!=null) {
    where+="AND username = '" + userName + "'";
  }
  if(componentName!=null) {
    where+="AND componentname = '" + componentName + "'";
  }
  if(componentAlias!=null) {
    where+="AND componentalias = '" + componentAlias + "'";
  }
  if(!where.equalsIgnoreCase("")) {
    where = where.substring(3);
    where = " WHERE " + where;
  }
  query = query + where;
  LOGGER.info("Query: " + query);
 
  Statement s = (Statement) conn.createStatement();
  ResultSet rs = s.executeQuery(query);

我如何使用 Speedment ORM 过滤器做到这一点？

Answer 1

在 Speedment 中非常相似。每次添加过滤器时，Stream 接口(interface)都会返回一个新的 Stream。您可以简单地将其存储在一个变量中，并像在您的代码中一样使用 if 语句。

Stream stream = instances.stream();
if (userName != null) {
    stream = stream.filter(Instance.USERNAME.equal(userName));
}

if (componentName != null) {
    stream = stream.filter(Instance.USERNAME.equal(componentName));
}

if (componentAlias != null) {
    stream = stream.filter(Instance.USERNAME.equal(componentAlias));
}

List<Instance> result = stream.collect(toList());