Add the Ability to Specify an Alias in a Table Object

[jeffgbutler]

This PR adds a new meta-model object AliasableSqlTable that can contain an alias to be used when a select statement is rendered.

Resolves #413

[coveralls]

Coverage remained the same at 100.0% when pulling 2a03903 on jeffgbutler:new-alias-strategy into 8fa2e76 on mybatis:master.

[djechelon]

Hi, I got this in my project but looks like it's not working for EXISTS queries.

Here is an example

amlObjectMapper.selectDistinct(select -> select
                        .join(amlAttachment, "attachment", on(amlObject.objectid, equalTo(amlAttachment.attachmentid)), and(amlObject.objecttypeid, equalTo(amlAttachment.attachmenttypeid)))
                        .where(amlObject.objecttypeid, isEqualTo(AmlObjectType.ATTACHMENT.getValue()))
                        .and(exists(select(of("1"))
                                .from(taxonomyControlAttachment, "tca")
                                .where(taxonomyControlAttachment.attachmentcontrolid, isEqualTo(taxonomyControlIdVersion))
                                .and(taxonomyControlAttachment.attachmentid, isEqualTo(amlAttachment.attachmentid))
                                .and(taxonomyControlAttachment.attachmenttypeid, isEqualTo(amlAttachment.attachmenttypeid))
                                .applyWhere(limitToTypes != null && limitToTypes.length > 0
                                        ? where -> where.and(amlAttachment.attachmenttype, isIn(limitToTypes))
                                        : x -> {
                                })
                        ))

Resulting query

select distinct AML_Objects.ObjectId,
                AML_Objects.ObjectTypeId,
                AML_Objects.ObjectUpdatedBy,
                AML_Objects.ObjectCreatedBy,
                AML_Objects.ObjectUpdated,
                AML_Objects.ObjectCreated
from AML_Objects
         join AML_Attachments attachment on AML_Objects.ObjectId = attachment.AttachmentId and
                                            AML_Objects.ObjectTypeId = attachment.AttachmentTypeId
where AML_Objects.ObjectTypeId = ?
  and exists(select 1
             from TAXO_TaxonomyControlAttachments tca
             where tca.AttachmentControlId = ?
               and tca.AttachmentId = AttachmentId
               and tca.AttachmentTypeId = AttachmentTypeId)

Expected query (fragment)

               and tca.AttachmentId = attachment.AttachmentId
               and tca.AttachmentTypeId = attachment.AttachmentTypeId)

This is likely because the referenced object amlAttachment is aliased only in the outer query. As you can see, table TaxonomyControlAttachments is aliased tca.

I can confirm, however, this fixes the self-join alias problem. For the join queries, of course.

[djechelon]

Please note this is not critical to our team as we could change the query in order to make it work. For now, we are not stuck

[jeffgbutler]

The aliases specified this way will not carry into to exists queries (or union queries either). You have a couple of options:

1. You could use a hard alias on the Attachment table aliasedAttachment = attachment.withAlias("attachment") and then use the aliasedAttachment table and its fields in the query. The aliasedAttachment object should do exactly what you want
2. You could explicitly qualify the columns in the exists query amlAttachment.attachmentid.qualifiedWith("attachment"). This is a bit wordier, but it will produce what you want without creating a separate table object

[jeffgbutler]

@djechelon I've created a new issue for aliases in exists queries - I should be able to solve this. You can track progress here: #437