从SQL查询获取表值

Question

我想从SQL查询中获取一些配置值：

通常，我使用以下Java代码从表列中获取数据：

PreparedStatement ps = null;

try
{
    ps = conn.prepareStatement("SELECT US.USER_ID, S1.DESCRIPTION, S1.DATA_TYPE, CASE WHEN S1.CONSTRAINED = 'TRUE' THEN AV.ITEM_VALUE "
        + " ELSE US.UNCONSTRAINED_VALUE END \"VALUE\", AV.CAPTION FROM USER_SETTING US INNER JOIN SETTING S1 ON US.SETTING_ID = S1.ID "
        + " LEFT OUTER JOIN ALLOWED_SETTING_VALUE AV ON US.ALLOWED_SETTING_VALUE_ID = AV.ID WHERE US.USER_ID = 234");

    ResultSet rs = ps.executeQuery();
    while (rs.next())
    {
        obj = new SystemConfigurationObj(
            rs.getString("SNMP_SERVER"),
            rs.getInt("PORT"),
            rs.getString("SNMP_USERNAME"),
            rs.getString("SNMP_PASSWORD"),
            rs.getBoolean("IS_SSL")
        );
    }
}

如何从每一行获取值并根据值类型进行转换？

我用这个表结构

    CREATE TABLE SETTING(
     ID INTEGER NOT NULL,
     DESCRIPTION TEXT,
     CONSTRAINED BOOLEAN,
     DATA_TYPE TEXT,
     MIN_VALUE TEXT,
     MAX_VALUE TEXT
    )
    ;

    ALTER TABLE SETTING ADD CONSTRAINT KEY34 PRIMARY KEY (ID)
    ;

    CREATE TABLE ALLOWED_SETTING_VALUE(
     ID INTEGER NOT NULL,
     SETTING_ID INTEGER,
     ITEM_VALUE TEXT,
     CAPTION TEXT
    )
    ;

    CREATE INDEX IX_RELATIONSHIP16 ON ALLOWED_SETTING_VALUE (SETTING_ID)
    ;


    ALTER TABLE ALLOWED_SETTING_VALUE ADD CONSTRAINT KEY35 PRIMARY KEY (ID)
    ;

    CREATE TABLE USER_SETTING(
     ID INTEGER NOT NULL,
     USER_ID INTEGER,
     SETTING_ID INTEGER,
     ALLOWED_SETTING_VALUE_ID INTEGER,
     UNCONSTRAINED_VALUE TEXT
    )
    ;

    CREATE INDEX IX_RELATIONSHIP15 ON USER_SETTING (SETTING_ID)
    ;

    CREATE INDEX IX_RELATIONSHIP17 ON USER_SETTING (ALLOWED_SETTING_VALUE_ID)
    ;

    ALTER TABLE USER_SETTING ADD CONSTRAINT KEY36 PRIMARY KEY (ID)
    ;

with
  allowed AS (
    INSERT INTO ALLOWED_SETTING_VALUE (id, setting_id, item_value, caption)
    VALUES 
    (123, 10, '#0000FF', 'Blue'), 
    (124, 10, '127.0.0.1', 'Yellow'), 
    (125, 10, '#FF00FF', 'Pink')
    RETURNING *),
  data(id, description, constrained, data_type, min_value, max_value, us_id, user_id, allowed_setting_value_id, unconstrained_value) as (
    VALUES
        (10, 'SMTP_SERVER', true, 'text', NULL, NULL, 5678, 234, (select id::Integer from allowed where caption = 'Yellow'), NULL),
        (11, 'SMTP_PORT', false, 'integer', '1', '65000', 7890, 234, NULL, '650'),
        (12, 'SNMP_USERNAME', false, 'text', '0', '9000', 8901, 234, NULL, 'username'),
        (13, 'SNMP_PASSWORD', false, 'text', '0', '9000', 8902, 234, NULL, 'password'),
        (14, 'IS_SSL', false, 'boolean', '0', '9000', 8903, 234, NULL, 'true')),
  settings as (
    INSERT INTO SETTING (id, description, constrained, data_type, min_value, max_value)
    SELECT id, description, constrained, data_type, min_value, max_value
    FROM data
    RETURNING *)
INSERT INTO USER_SETTING (id, user_id, setting_id, allowed_setting_value_id, unconstrained_value)
SELECT d.us_id, d.user_id, s.id, d.allowed_setting_value_id, d.unconstrained_value
FROM settings s
JOIN data d ON (d.id = s.id);

Answer 1

您可以先获取data_type，然后将其打开，例如：

    ResultSet rs = ...;
    Map<String, Object> values = new HashMap<String, Object>();
    while (rs.next()) {
        Object o = null;
        String type = rs.getString("data_type");
        switch(type) {
        case "text":
            o = rs.getString("value");
            break;
        case "boolean":
            o = "true".equalsIgnoreCase(rs.getString("value"));
            break;
        case "int":
            o = rs.getInt("value");
            break;
        }
        values.put(rs.getString("description"), o);
    }

然后您可以像创建对象

    new SystemConfigurationObj(
        (String)values.get("SNMP_SERVER"),
        (int)values.get("SMTP_PORT"),
        (String)values.get("SNMP_USERNAME"),
        (String)values.get("SNMP_PASSWORD"),
        (boolean)values.get("IS_SSL")
    );