使用NamedParamterJdbcTemplate对象指定要查询的mysql字段和值

Question

I am currently in the process of learning the Java Spring Framework, and I am having difficulty understanding why the following query is failing to return any results from the database.

I am ultimately trying to create a where method in my OffersDAO class that allows my to query on a specific field, for a specific value.

public List<Offer> where(String field, String value){

    MapSqlParameterSource params = new MapSqlParameterSource();
    params.addValue("field", field);
    params.addValue("value", value);
    String sql = "select * from offers where :field = :value";
    return jdbc.query(sql, params, new RowMapper<Offer>(){

        public Offer mapRow(ResultSet rs, int arg1) throws SQLException {
            Offer offer = new Offer();
            offer.setId(rs.getInt("id"));
            offer.setName(rs.getString("name"));
            offer.setText(rs.getString("text"));
            offer.setEmail(rs.getString("email"));
            return offer;   
        }

    });

}

I am able to successfully query the database for results when I specify the field explicitly, as follows:

String sql = "select * from offers where name = :value";

Obviously there is something wrong with specifying the field name dynamically. My guess is it is most likely due to the fact that the field key is being inserted as a mysql string (with '' ), when in fact mysql expects a column name for the :field placeholder.

My questions are as follows:

1. Is there a way to accomplish what I am attempting to do above, using the jdbc NamedParameterJdbcTemplate class?

2. If I cannot accomplish the above, by what means can I?

Thank you

Edit: No exceptions are thrown. In the case when I am attempting to supply the column name, a empty result set is returned.

Answer 1

You can't specify the field name in a parameter - only the field value. Since you know the DB schema when you're writing the code, this shouldn't be much of a problem.

Answer 2

What about include all possible fields in the filter but restricting their usage by field name param. Like this:

select * from offers where 
('name'=:field and name = :value)
OR
('field2'=:field and field2 = :value)
OR
('field3'=:field and field3 = :value)

Answer 3

I don't know how You can implement it with spring (I mean use variable column names) but I can suggest to use the following principle.

Keep your query like template:

String sql = "select * from offers where ##field = :value";

And every time before execution replace ##value parameter with the column You want. And then You are gone.