Constructing resultMap to create different instances for the same collection
(Using MyBatis v3.0.4.) I have a problem that I do not know how to solve. My object model is:
Location.java
public class Location {
// ... other content
private List addresses;
// ... other content
}
Address.java
public class Address {
public enum Type { POSTAL, POBOX, INPUT, CLEANSED }
private Type type;
private String line1;
// ... other content
}
My SQL is:
SELECT
// ... other content
postal_address_line_1,
postal_address_line_2,
po开发者_Python百科stal_address_city,
cleansed_address_line_1,
cleansed_address_line_2,
cleansed_address_city,
// ... other content
How would I construct a resultMap
that would plug the appropriate
columns into an address instance of the correct type and added to the
same list in Location.java? I would like to avoid having to add
another instance variable to Location.java just to hold a different
type of address.
Use a discriminator tag in your result map.
Look at the mybatis user guide. Search for "discriminator" you see more informations.
<resultMap id="vehicleResult" type="Vehicle">
<id property=”id” column="id" />
<result property="sharedPropA" column="shared_column"/>
<discriminator javaType="int" column="address_type">
<case value="1" resultMap="postalResultMap"/>
<case value="2" resultMap="inputResultMap"/>
<case value="3" resultMap="cleanResultMap"/>
<case value="4" resultMap="whatIsaCleansedAddressResultMap"/>
</discriminator>
</resultMap>
Addition 1:
You need to select the addresses as different rows.
i.e
select
postal_address_line_1 as line1,
postal_address_line_2 as line2,
postal_address_city as city,
type as 'POSTAL'
....
union
select
postal_address_line_1 as line1,
postal_address_line_2 as line2,
postal_address_city as city,
type as 'CLEANSED'
.....
then the built in enum type handler should set the type correctly.
Along the lines of Andy Pryor's suggestion, I was able to solve the problem by updating my SQL statement to something like the following:
SELECT
// ... other content
'POSTAL' as Postal_Address_Type,
postal_address_line_1,
postal_address_line_2,
postal_address_city,
'CLEANSED' as Cleansed_Address_Type,
cleansed_address_line_1,
cleansed_address_line_2,
cleansed_address_city,
// ... other content
Then update my resultMap
to the following:
<resultMap ...>
//... other content
<association property="postalAddress" javaType="com.x.y.z.Address">
<result property="type" column="Postal_Address_Type"/>
<result property="line1" column="Address_Part_1_Name"/>
<result property="line2" column="Address_Part_2_Name"/>
//...other content
</association>
<association property="cleansedAddress" javaType="com.x.y.z.Address">
<result property="type" column="Cleansed_Address_Type"/>
<result property="line1" column="Address_Part_1_Name"/>
<result property="line2" column="Address_Part_2_Name"/>
//...other content
</association>
</resultMap>
Finally, within my Address
class I am able to have setType(Type)
and the inbuilt enumerated type handler does the magic. Within the Location
class I can just have one list of instances of Address
and the various setXXXAddress() methods can add to this list appropriately.
It is unfortunate that I cannot plug the columns into some sort of factory class but putting hard-coded types into the SQL statement isn't too dirty, in my opinion. The disadvantage is that I have introduced coupling between the domain model's Address.Type
values and the SQL statement but this is kind of already there given that the resultMap
SQL XML needs to hold the names of instance variables in the Address
class anyway.
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