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Welcome

to

the

Apache

Tuscany

Java

DAS

RDB

FAQ

page.

Please

help

to

keep

the

information

on

this

page

current.

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RDB DAS thread safety RDB DAS thread safety

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RDB DAS thread safety

DAS design should support thread safety, but we have done no explicit testing on this area.
Initializing a DAS and using across multiple DAS calls should be OK and safe as long as you are using the same config file. I'd recommend initializing the DAS in a sync method tough.

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Migration from M2 Migration from M2

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Migration from M2

I'm getting "Feature 'Config' not found." after migrating my application for after M2 codebase.

There was a change (see http://issues.apache.org/jira/browse/TUSCANY-899).

To

fix

this,

changed

the

attribute

"xmlns"'s

value

of

the

"config"

tag

to

"http:///org.apache.tuscany.das.rdb/config.xsd".

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transaction management transaction management

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Handling internal/external

transaction

management

In

DAS

Config,

element

ConnectionInfo

has

a

boolean

attribute

managedtx

(default

true).

If

it

is

true,

DAS

runtime

manages

transaction

otherwise

the

caller

is

supposed

to

manage

transaction.

In

cases,

when

the

connection

is

externally

passed

(config

file

does

not

specify

ConnectionInfo),

the

managedtx

attribute

default

value

(

true)

is

assumed.

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handling parent/child relationship handling parent/child

relationship

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Handling parent/child

relationship

Question: If two tables have a parent-child

relationship

but

the

query

result

set

contains

only

columns

from

one

table,

does

RDB

DAS

result

DataGraph

contain

data

from

both

parent

and

child

table?

The

RDB

DAS

will

only

populate

a

graph

with

data

returned

from

the

used

query.

If

you

want

a

graph

that

contains

data

from

related

tables

then

the

query

provided

must

return

that

data

(typically

a

join).

The

relationship

tests

in

the

test

suite

demonstrate

this.

Question: If

two

tables

have

a

parent-child

relationship

and

the

query

result

set

contains

columns

from

both

tables,

is

the

relationship

analyzed

by

DAS

when,

1. DAS

1. Config

1. explicitly

1. defines

1. relationship

2. DAS

1. Config

1. does

1. not

1. explicitly

1. define

1. relationship?

DAS

supports

some

Convention

over

Configuration

when

it

comes

to

supporting

implied

relationships.

http://cwiki.apache.org/confluence/display/TUSCANY/ConventionOverConfiguration

http://cwiki.apache.org/confluence/display/TUSCANY/ForeignKeyRepresentationAndManagement

http://cwiki.apache.org/confluence/display/TUSCANY/WorkingWithRelationships

Also,

see

test:

ImpliedRelationshipTests.testAddNewOrder()

So,

in

summary,

if

the

query

has

a

where

clause

specifying

the

relationship,

there

is

no

need

to

have

any

relationship

definition

in

config

file

as

long

as

the

column

names

(PK,

FK)

follow

the

naming

conventions.

In

the

absence

of

naming

conventions,

the

relationship

needs

to

be

explicitly

defined

in

the

config,

so

that

the

query

result

is

mapped

against

it

and

the

necessary

result

DataGraph

is

represented

reflecting the relationship.

Question: When there is 1:n relationship between 2 tables, say Department:Employee, and there is a DataGraph with this relationship present, can one Employee DataObject from this graph be associated with 2 different Department DataObjects, using DAS Java Client? i.e. can 1:n relationship be changed to n:n using SDO?_

No, when this is attempted, SDO maintains referential integrity. e.g.
If you have a dept1 with emp1 and then execute:
dep2.getEmployees.add(emp1)
the graph will automatically remove emp1 from dep1's list of employees and
you are left with valid 1:m relationship.

Question: In case of parent-child relationship, how to traverse back and forth?

If by Convention over Configuration/from DAS Config there is a name to a relationship, the opposite relationship is named with _opposite appended to it.

e.g. Consider two tables (CUSTOMER, ORDER) each with a PK named "ID". Also, ORDER has a FK named CUSTOMER_ID. The DAS recognizes this convention and assumes a one:many relationship between CUSTOMER and ORDER. In the fully dynamic case, a read of CUSTOMER and ORDER tables using a join will result in a graph of CUSTOMER DataObjects along with their related ORDERS.(name of relationship is ORDERS now.)

The property for the CUSTOMER Types list of ORDERs is named "ORDER" so:
DataObject order = cust.getDataObject("ORDER1");
The name of the property in the ORDER Type that references the parent CUSTOMER, is
DataObject cust = order.getDataObject("CUSTOMER_opposite")

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mapping mapping

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How does DAS handle mapping between DataGraph properties and Database Metadata like table name, column name etc. during disconnected processing.

DAS supports this mapping using DAS Config and in the absence of that using Convention over Configuration.
http://cwiki.apache.org/confluence/display/TUSCANY/ConventionOverConfiguration

.

DataObject

graph

change

summary

contains

old

as

well

as

modified

values.

Using

this

change

summary

and

config/conventions

DAS

can

support

the

necessary

mapping.

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no PK defined no PK defined

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no PK defined

Does DAS support working with tables that have no PK defined?

DAS mandates PK for any table, either specified in DAS Config or by following convention. In absence
of both of these, DAS throws an error. Having PK ensures uniqueness of Data Object - returned as query result.

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RDB DAS support for generated keys RDB DAS support for generated keys

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RDB DAS support for generated keys

This is supported for INSERT operation - either explicit insert (SQL INSERT statement as DAS command) or generated insert.
In case of generated insert, the DAS config needs to have Column element having attribute "generated" set to "true". This attribute is not needed in case of explicit insert.
In case of generated insert, "generated" attribute from Column element in Config is checked to form the appropriate insert statement. The jdbc supported PreparedStatement.getGeneratedKeys() is used to fetch the values being generated by the database. In case of generated insert, the value thus returned is set in DataGraph.

New boolean attribute added in Config - "generatedKeysSupported". User can set true/false for this in Config. If not set in Config, JDBC Metadata API check supportsGetGeneratedKeys() is done to detect whether to use auto generated keys during INSERT.

Note: For Derby, always assumed generatedKeysSupported=TRUE. This is because current Derby API return FALSE for supportsGetGeneratedKeys(), as it is partially implemented, but in DAS context, this support is sufficient.

This gived user flexibility to turn on/off support for database generated keys during INSERT based on the
database vendor/driver version in use.

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How DAS works with Dataobjects How DAS works with Dataobjects

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How DAS works with Dataobjects

DAS can get DataObject using Dynamic approach or Static approach. In Dynamic approach the query result set is used to form the DataObject. In static approach, DAS Config's DataObjectModel attribute needs a valid value, using which the DataObjects are created.
For more details see http://cwiki.apache.org/confluence/display/TUSCANY/Graph+Merge

.

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Optimistic Concurrency Control Optimistic Concurrency Control

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What is Optimistic Concurrency Control?

See details on http://cwiki.apache.org/confluence/display/TUSCANY/OptimisticConcurrencyControl

By

default

OCC

is

ON.

With

this,

in

generated

UPDATE

statement,

any

column

undergoing

change

also

gets

included

in

the

WHERE

clause.

Other

than

that,

in

DAS

Config,

in

<Table>

element

,

the

<Column>

element

can

have

two

boolean

attributes:-

managed(default

true),

collision

When

collision=true

for

a

column,

during

UPDATE

statement

generation,

that

column

is

included

in

the

WHERE

clause.

When

managed=true

for

a

column,

during

UPDATE

statement

generation,

that

column

(needs

to

be

BigDecimal)

value

is

incremented

by

1

and

used

in

the

SET

clause

in

UPDATE.

managed=true,

is

effective

only

when

collision=true,

else

managed

attribute

value

is

ignored.

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keyRestricted keyRestricted

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What is the purpose of many and keyRestricted attributes in Relationship?

many=true allows for 1:n relationship. If it is false, it's 1:1 relationship. In case of 1:1 relationship, if keyRestricted is not specified, the link (relationship) between the parent and child rows can be broken, by setting the parentKeyTable's row to null/deleting the row. Also, a different parent row can be associated to the child row, which has one pre-existing parent row association. If keyRestricted=true, this kind on change in existing relationship is not allowed, user will get exception 'Can not modify a one to one relationship that is key restricted'.

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paging paging

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what is paging capability?

What is currently available in DAS is detailed on http://cwiki.apache.org/confluence/display/TUSCANY/WorkingWithPaging
Other than sequential page access(pager.next(), pager.previous()), random access is also
allowed using pager.getPage(number).

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ResultSet ResultSet

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Example to define the ResultSet shape Definition for a join in DAS

Doing:

Select a.dept_name, b.employee_name
from dept a, emp b
where a.id = b.dept_id (+)

How do I define an Explicit ResultSet shape definition for the resultset from a join?

You can find some information on the DAS User Guide 1. There are
couple test cases that also show this working, here is one test case
2 and it's config file 3.

Allow passing ResultDescriptor to Dynamic Commands. i.e. Command x = das.createCommand("y");
x can have set/get of single/list of ResultDescriptors. Useful for databases like Oracle
which require user to pass ResultDescriptor and for cases when the commands are created dynamically
using createCommand()

1 http://incubator.apache.org/tuscany/explicit-resultset-shape-definition.html
2 https://svn.apache.org/repos/asf/incubator/tuscany/java/das/rdb/src/test/java/org/apache/tuscany/das/rdb/test/RelationshipTests.java
3 https://svn.apache.org/repos/asf/incubator/tuscany/java/das/rdb/src/test/resources/companyMappingWithResultDescriptor.xml

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blob blob

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Does DAS support datatypes like Blob?

RDB DAS supports SQL Data Types like Blob, Clob, ByteArray, Array.

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namedParams namedParams

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Does DAS support named parameters passing?

User can do Command.setParameter(String name, Object value), getParameter(String name). Indexed set/getParameter() is available as before. Also <create>, <update>, <delete> from Config support named parameters.