Merge Scripting and Parameterization phases in dynamic sql

Currently dynamic sql is managed in two phases, one for scripting and one for sql parameterization. This leads to two different languages in a dynamic sql at the same time and is a common source of mistakes.

For example, using velocity scripting we can do something like:

SELECT * from mytable Where mycolumn = '$_parameter.mymethod($_parameter.value)'

but we can’t do:

SELECT * from mytable Where mycolumn = @{$_parameter.mymethod($_parameter.value)}

Because SQL parameter binding language is not velocity, but a propietary binding language.

The problem goes worst in loops, because the scope of the scripting variables and sql parameter are not the same. So <bind /> will not work in loops as expected.

My proposal is to extract any sql parameter in the scripting phase and cache it in the BoundSql object as proposed some time ago by Eduardo, then the sql parameterization will use the already extracted values directly by index, so we can use arbitrary scripting expressions.

For example:

SELECT * from mytable Where mycolumn = $sql.bind($_parameter.mymethod($_parameter.value))

the hypothetical $sql.bind method should support more parameters like type (IN,OUT,INOUT), jsdbType, etc…

Also in the case of velocity, the method can be replaced by a more friendly syntax (macro):

#set ($p = $_parameter)
SELECT * from mytable Where mycolumn = #param( $p.mymethod( $p.value ) )

[Drizzt321]

Ok, for those who find this, I solved my problem by having a utility method which returns a Map with the dynamic field name/value set, and iterated through the map. Here’s a mapper fragement. getModifiedFields() returns a Map<String,Object>. I have it with a bind so that I can be sure that it iterates the same way for each for loop. For actual implementation, I’m using a TreeMap, but any kind of map with a consistent iteration should work fine.

INSERT INTO ${tableName}
<bind name="data" value="entity.getModifiedFields()"/>
<foreach item="value" index="name" collection="data" open="(" separator="," close=")">
    ${name}
</foreach>
VALUES
<foreach item="value" index="name" collection="data" open="(" separator="," close=")">
    #{value}
</foreach>

[Drizzt321]

Ah, I see. That’s too bad. I’m actually a little surprised this hasn’t come up earlier than now. Maybe I’ll end up having to change my Mapper configs to try and work around it so I won’t have this bind problem so I can properly use prepared statement output.