xialvjun created METAMODEL-147:
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Summary: API, Maven CodeGenerator
Key: METAMODEL-147
URL: https://issues.apache.org/jira/browse/METAMODEL-147
Project: Apache MetaModel
Issue Type: Wish
Affects Versions: 4.4.0
Reporter: xialvjun
I sended an email to [email protected] last night. But now I found jira
site of metamodel, so paste the email here.
I've searched http://wiki.apache.org/metamodel/ with keyword "subquery", but
there is no result.
I used to think if org.apache.metamodel.query.Query implements
org.apache.metamodel.schema.Table so I can do it like
dataContext.query().from(query), but it doesn't.
So I ask you how to do SubQuery in MetaModel.
In fact, I think the api of MetaModel can do a big change, like this:
{code}
TableLike = dataContext.query().from(TableLike... tables)
TableLike = dataContext.query().from(TableLike... tables).select(ColumnLike...
columns)
Filter = ColumnLike.operator(value)
dataContext.query().from(TableLike... tables).select(ColumnLike...
columns).where(Filter... filters).groupBy(ColumnLike... columns)
DataSet ds = TableLike.execute();
{code}
There are 3 main interfaces: TableLike , ColumnLike , Filter.
query, table, view are all TableLike;
column in a query, column in a table are all ColumnLike;
filter is generated by ColumnLike...
And if the Column Type can be represent by the class of Column, things may be
better.
Maybe we can't make Column a generic class like Column<Integer>, because we
can't use it like Column<Person>(wait, wait, wait, maybe we can if Person is
just a java bean.... WOW, so it seems that TableLike is in fact a subclass of
ColumnLike, ehh, it's a little complex, leave it).... So we can have some
simple column class like IntegerColumn, StringColumn, DateColumn.....
By the way, I think a code generator maven plugin is needed. I usually
manually create a DB class which has static members of all the Tables and
Columns, then I can use them without string literals to represent table or
column which has a using expirence like jooq or empire-db. I believe a maven
code generation plugin will do better. It can also create pojo class from
database schema using underline naming method to camel naming method... So when
we get a Dataset dataSet object, we can just like
dataSet.extract(List<Person>.class) to get the data.
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