where clause as a parameter - nhibernate

Question

IN converting over a legacy application we need to convert named query to nhibernate. The problem is that the where clause is being set.
here is the mapping
<resultset name="PersonSet">
<return alias="person" class="Person">
<return-property column="id" name="Id" />
<return-property column="ssn" name="Ssn" />
<return-property column="last_name" name="LastName" />
<return-property column="first_name" name="FirstName"/>
<return-property column="middle_name" name="MiddleName" />
</return>
</returnset>
<sql-query name="PersonQuery" resultset-ref="PersonSet" read-only="true" >
<![CDATA[
SELECT
person.ID as {person.Id},
person.SSN as {person.Ssn},
person.LAST_NAME as {person.LastName},
person.MIDDLE_NAME as {person.MiddleName},
person.FIRST_NAME as {person.FirstName},
FROM PERSONS as person
where :value
]]>
</sql-query>
and the c# code:
String query = "person.LAST_NAME = 'Johnson'";
HibernateTemplate.FindByNamedQueryAndNamedParam("PersonQuery", "value", query);
The error:
where ?]; ErrorCode []; An expression of non-boolean type specified in a context where a condition is expected, near '#p0'.

Answer 1

This doesn't work because you try to replace :value with "person.LAST_NAME = 'Johnson'" wanting that the query becomes
SELECT person.ID, person.SSN, person.LAST_NAME, person.MIDDLE_NAME, person.FIRST_NAME
FROM PERSONS as person
where person.LAST_NAME = 'Johnson'
This won't work. You can only replace the 'Johnson' part dynamically not the whole condition. Thus what really gets generated is
SELECT person.ID, person.SSN, person.LAST_NAME, person.MIDDLE_NAME, person.FIRST_NAME
FROM PERSONS as person
where 'person.LAST_NAME = \'Johnson\''
Which obviously isn't a valid condition for the WHERE-part as there is only a literal but no column and operator to compare the field to.
If you only have to match against person.LAST_NAME rewrite the xml-sql-query to
<sql-query name="PersonQuery" resultset-ref="PersonSet" read-only="true" >
<![CDATA[
SELECT
...
FROM PERSONS as person
where person.LAST_NAME = :value
]]>
</sql-query>
And in the C# code set
String query = "Johnson";
If you need to dynamically filter by different columns or even multiple columns at a time use filters. e.g. like this (i made a few assumptions on you hibernate-mapping file)
<hibernate-mapping>
...
<class name="Person">
<id name="id" type="int">
<generator class="increment"/>
</id>
...
<filter name="ssnFilter" condition="ssn = :ssnValue"/>
<filter name="lastNameFilter" condition="lastName = :lastNameValue"/>
<filter name="firstNameFilter" condition="firstName = :firstNameValue"/>
<filter name="middleNameFilter" condition="middleName = :middleNameValue"/>
</class>
...
<sql-query name="PersonQuery" resultset-ref="PersonSet" read-only="true" >
...
FROM PERSONS as person
]]>
</sql-query>
<!-- note the missing WHERE clause in the PersonQuery -->
...
<filter-def name="ssnFilter">
<filter-param name="ssnValue" type="int"/>
</filter-def>
<filter-def name="lastNameFilter">
<filter-param name="lastNameValue" type="string"/>
</filter-def>
<filter-def name="middleNameFilter">
<filter-param name="midlleNameValue" type="string"/>
</filter-def>
<filter-def name="firstNameFilter">
<filter-param name="firstNameValue" type="string"/>
</filter-def>
</hibernate-mapping>
Now in your code you should be able to do
String lastName = "Johnson";
String firstName = "Joe";
//give me all persons first
HibernateTemplate.FindByNamedQuery("PersonQuery");
//just give me persons WHERE FIRST_NAME = "Joe" AND LAST_NAME = "Johnson"
Filter filter = HibernateTemplate.enableFilter("firstNameFilter");
filter.setParameter("firstNameValue", firstName);
filter = HibernateTemplate.enableFilter("lastNameFilter");
filter.setParameter("lastNameValue", lastName);
HibernateTemplate.FindByNamedQuery("PersonQuery");
//oh wait. Now I just want all Johnsons
HibernateTemplate.disableFilter("firstNameFilter");
HibernateTemplate.FindByNamedQuery("PersonQuery");
//now again give me all persons
HibernateTemplate.disableFilter("lastNameFilter");
HibernateTemplate.FindByNamedQuery("PersonQuery");
If you need still more dynamic queries (e.g. even changing the operator (=, !=, like, >, <, ...) or you have to combine restrictions logically (where lastname = "foo" OR firstname" = "foobar") then it's definitly time to look into the
Hibernate Criteria API

Answer 2

I'm unfamiliar with this HibernateTemplate syntax, but it looks like you're querying the original fieldname in SQL rather than the alias. Try this:
String query = "person.LastName = 'Johnson'";
or, maybe:
String query = "[person.LastName] = 'Johnson'";
or, possibly:
String query = "{person.LastName} = 'Johnson'";
Depends what sort of pre-processing is going on before the final SQL query is sent to the server.

Answer 3

That's because :value is a bind variable in the query; you cannot simply replace it with a string that contains an arbitrary string (that would become part of the query), only with an actual value. In your case, the value is "person.LAST_NAME = 'Johnson'", which is actually a string, not a boolean value. Boolean values would be true or false, both of which are rather useless for what you try to archive.
Bind variables more-or-less replace literals, not complex expressions.