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POJava Enums with Generic Classes
 

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    <p>I am switching gears from the interpreted world and I am trying to replicate a pattern I have used in the passed with great success but in Java.</p> <p>The short of it is I am making a custom DAO (not using Hibernate or anything like that...ultimately it will be generic to handle different database engines (SQL and NoSQL). For breaking into I am just using a MySQL/ Prepared Statements.</p> <p>I want to basically define a DataMapper object that is responsible for mapping the field of a record to the fields in a database. I am trying to encapsulate any redundant logic for implementation details of transforming a type to the format the database expects. In the DataMapper I am trying to utilize an enum to list the fields:</p> <pre><code>public abstract class AbstractDataMapper&lt;X&gt; { public static abstract class Field&lt;Y&gt; { protected String name; public Field(String name) { this.name = name; } public String getName() { return this.name; } public abstract void setValue(PreparedStatement stmt, int parameterIndex, Y value) throws SQLException; public abstract Y getValue(ResultSet rset) throws SQLException; } public static class IntegerField extends AbstractDataMapper.Field&lt;Integer&gt; { public IntegerField(String name) { super(name); } @Override public void setValue(PreparedStatement stmt, int parameterIndex, Integer value) throws SQLException { stmt.setInt(parameterIndex, value.intValue()); } @Override public Integer getValue(ResultSet rset) throws SQLException { return new Integer(rset.getInt(this.name)); } } } public class UserDataMapper extends AbstractDataMapper&lt;UserDataRecord&gt;{ public static enum Field { entryId(new AbstractDataMapper.IntegerField("entryid")); AbstractDataMapper.Field&lt;?&gt; field = null; Field(AbstractDataMapper.Field&lt;?&gt; field) { this.field = field; } public AbstractDataMapper.Field&lt;?&gt; getField() { return this.field; } public String getName() { return this.field.getName(); } } </code></pre> <p>Obviously I tried to truncate the example to the meaningful parts. The client code for exercising this </p> <pre><code> public int insert(UserDataRecord user) { ... final String query = "INSERT INTO users SET " + UserDataMapper.Field.entryId.getName() + " = ? "; stmt = conn.prepareStatement(query); UserDataMapper.Field.entryId.getField() .setValue(stmt, 1, user.getEntryId()); } </code></pre> <p>The issue I am encountering is with the last line. I am trying to use the generic object associated with the <code>entryId</code> enum to use it's special setValue function which handles getting the Integer into the proper format. My IDE is giving me the following error: The method setValue(PreparedStatement, int, capture#13-of ?) in the type AbstractDataMapper.Field is not applicable for the arguments (PreparedStatement, int, Integer).</p> <p>I am sure I could get into a series of crazy typecasts...but at that point it would probably just be easier to expose the translation details.</p> <p>Any ideas on getting this to work or a modification to this pattern that is better? </p>
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