IN 子句和占位符 [英] IN clause and placeholders

问题描述

我正在尝试在 Android 中执行以下 SQL 查询:

I'm attempting to do the following SQL query within Android:

    String names = "'name1', 'name2";   // in the code this is dynamically generated

    String query = "SELECT * FROM table WHERE name IN (?)";
    Cursor cursor = mDb.rawQuery(query, new String[]{names});

但是，Android 不会用正确的值替换问号.我可以执行以下操作，但是，这并不能防止 SQL 注入:

However, Android does not replace the question mark with the correct values. I could do the following, however, this does not protect against SQL injection:

    String query = "SELECT * FROM table WHERE name IN (" + names + ")";
    Cursor cursor = mDb.rawQuery(query, null);

我怎样才能解决这个问题并能够使用 IN 子句?

How can I get around this issue and be able to use the IN clause?

推荐答案

"?, ?, ..., ?" 形式的字符串可以是动态创建的字符串并且安全放入原始SQL查询中(因为它是一种限制形式，不包含外部数据)，然后占位符就可以正常使用了.

A string of the form "?, ?, ..., ?" can be a dynamically created string and safely put into the original SQL query (because it is a restricted form that does not contain external data) and then the placeholders can be used as normal.

考虑一个函数 String makePlaceholders(int len) 返回 len 用逗号分隔的问号，然后:

Consider a function String makePlaceholders(int len) which returns len question-marks separated with commas, then:

String[] names = { "name1", "name2" }; // do whatever is needed first
String query = "SELECT * FROM table"
    + " WHERE name IN (" + makePlaceholders(names.length) + ")";
Cursor cursor = mDb.rawQuery(query, names);

只需确保传递与位置一样多的值.SQLite 中默认的最大主机参数限制是 999 - 至少在正常构建中，不是确定 Android :)

Just make sure to pass exactly as many values as places. The default maximum limit of host parameters in SQLite is 999 - at least in a normal build, not sure about Android :)

这是一种实现:

String makePlaceholders(int len) {
    if (len < 1) {
        // It will lead to an invalid query anyway ..
        throw new RuntimeException("No placeholders");
    } else {
        StringBuilder sb = new StringBuilder(len * 2 - 1);
        sb.append("?");
        for (int i = 1; i < len; i++) {
            sb.append(",?");
        }
        return sb.toString();
    }
}

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