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multiple columns in parent to use same child table to save data in JPA

I have a requirement where I have to save employee detail to a child table, employee data remains the same for multiple parent records (columns as well), I want to use the existing child table to insert if not present and update if already present, how I can do that using Spring JPA / hibernate?
Parent Table
|id|project_id|owner_emp_id|developer_emp_id|lead_emp_id|tester_emp_id|
|:---- |:------:| -----:|:---- |:------:| -----:|
| 1 | 100 | emp_10 | emp_20 | emp_20 | emp_30 |
| 2 | 200 | emp_11 | emp_21 | emp_22 | emp_30 |
employee child table
|emp_id|first_name|olast_name|email|phone|
|:---- |:------:| -----:|:---- |:------:|
| emp_10 |..| .. | .. | .. |
| emp_20 | .. | .. | .. | .. |
| emp_30 | .. | .. | .. | .. |
| emp_11 | .. | .. | .. | .. |
| emp_21 | .. | .. | .. | .. |
| emp_22 | .. | .. | .. | .. |
from the above example when saving the child table during 1st record emp_20 data need to save only once. similarly, the 2nd record insert emp_30 already presents an update or ignores saving it, how to do this in JPA?

Define an entity via a custom SQL query in Hibernate 5.1

I'm working with a non normalized 3rd party database meaning I cannot change the schema. I'm trying to map the tables to JPA entities using Hibernate 5.1
There are 2 simple tables A and B:
| A_ID(pk) | | B_ID(pk) |
------------- -------------
| 1 | | 1 |
------------- | 2 |
-------------
Table C has a composite primary key and has a Many-To-One relation to Table A:
| A_ID(pk&fk) | QUANTITY(pk) | VALID_FROM(pk) |
---------------------------------------------------
| 1 | 1 | 2017-05-21 |
| 1 | 1 | 2018-01-01 |
| 1 | 2 | 2017-05-21 |
Table D has a composite primary key:
| A_ID(pk&fk) | QUANTITY(pk) | VALID_FROM(pk) | B_ID(pk&fk) |
--------------------------------------------------------------------
| 1 | 1 | 2018-01-21 | 1 |
| 1 | 2 | 2018-01-21 | 1 |
| 1 | 2 | 2018-05-01 | 2 |
the VALID_FROM column is not part of the join condition between the tables and can take up any value.
I'm trying to set up a relation between Table C and D but because of the VALID_FORM primary key component they cannot be modelled with Many-To-One. And since there is no join table they cannot be modelled with Many-To-Many either.
The best solution would be to create a view like
CREATE VIEW C_NORM AS
SELECT DISTINCT A_ID, QUANTITY
FROM TABLE_C;
which would produce view C_NORM:
| A_ID(pk&fk) | QUANTITY(pk) |
----------------------------------
| 1 | 1 |
| 1 | 2 |
Creating the C_NORM entity on this view could have
a One-To-Many relation with Table C
and another One-To-Many relation with Table D
but I cannot change the schema thus I cannot create a new view.
Is there any way to define an entity as a class with annotations that is basically based on a native SQL query rather than a view or table in the DB?

No that's not possible and it doesn't make sense.
Entities are for update, insert and delete. If you don't want to do any of these operations you shouldn't use entities.
You can use the #SqlResultSetMapping to map a result of a native query to a class
Query q = em.createNativeQuery(
"SELECT c.id, c.name, COUNT(o) as orderCount, AVG(o.price) AS avgOrder " +
"FROM Customer c " +
"JOIN Orders o ON o.cid = c.id " +
"GROUP BY c.id, c.name",
"CustomerDetailsResult");
#SqlResultSetMapping(name="CustomerDetailsResult",
classes={
#ConstructorResult(targetClass=com.acme.CustomerDetails.class,
columns={
#ColumnResult(name="id"),
#ColumnResult(name="name"),
#ColumnResult(name="orderCount"),
#ColumnResult(name="avgOrder", type=Double.class)})
})
Or alternatively use QLRM: https://github.com/simasch/qlrm

Spring JPA OneToMany with composite Key mapping

I am having issues mapping the following using spring JPA. Let's say I have a order table which has two primary keys. one is a foreign key to customer and another is a foreign key to order Type as seen below:
Customer
+----+------+--+
| id*| name | |
+----+------+--+
| 1 | Joe | |
+----+------+--+
Order
+------------+-------------+
| customerId | orderTypeId |
+------------+-------------+
| 1 | 1 |
+------------+-------------+
OrderType
+----+--------+
| id | type |
+----+--------+
| 1 | online |
+----+--------+
the idea is each customer has a one to many relationship with Orders. the primary key of orders is a combination of the two foreign keys.
any help would be appreciated.

Java Collections Optimization

I'm working on a java application that connects to database to fetch some records, processes each records and updates record back to the db table.
Following is my db schema (with sample data):
Table A: Requests
| REQUESTID | STATUS |
-------------------------
| 1 | PENDING|
| 2 | PENDING|
Table B: RequestDetails
| DETAILID | REQUESTID | STATUS | USERID |
---------------------------------------------
| 1 | 1 | PENDING | RA1234 |
| 2 | 1 | PENDING | YA7266 |
| 3 | 2 | PENDING | KAJ373 |
Following is my requirement:
1) Fetch Request along with pending status along with request data from both tables
I'm using below query for this:
SELECT Requests.REQUEST_ID as "RequestID",RequestDetails.USERID as "UserID",RequestDetails.DETAILID as "DetailID"
FROM Requests Requests
JOIN RequestDetails RequestDetails
ON (Requests.REQUESTID=RequestDetails.REQUESTID AND Requests.REQUEST_STATUS='PENDING' AND RequestDetails.STATUS='PENDING')
2) I'm using a HashMap<String, List<HashMap<String,String>> to store all the values
3) Iterate over each request and get details List<HashMap<String,String>>
Perform action for each detail record and update status
4) After all detail records are processed for a request, update status of the request on requests table
The end state should be something like this:
Table A: Requests
| REQUESTID | STATUS |
-------------------------
| 1 | PENDING|
| 2 | PENDING|
Table B: RequestDetails
| DETAILID | REQUESTID | STATUS | USERID |
---------------------------------------------
| 1 | 1 | PENDING | RA1234 |
| 2 | 1 | PENDING | YA7266 |
| 3 | 2 | PENDING | KAJ373 |
My question is: the collection I'm using is quite complex ("HashMap<String, List<HashMap<String,String>>"). Is there any other efficient way to do this?
Thank you,
Sash

I think you should use class something like,
Class RequestDetails{
int detailId;
int statusId;
String status;
String userId;
}
instead of map HashMap<String, List<HashMap<String,String>> you should use HashMap<String, RequestDetails>That has advantages like, code simplicity and also when you working with huge data and you need to modify string it is always better to avoid using String data-type as it is immutable and decrease your performance.
Hope this helps.

Above all that and what Darshan suggested, you must override the hashCode and equals method too, the reason is its the basic contract while dealing with HashMap and it will also increase the performance too.

How do I selectively update columns in a table when using LOAD DATA INFILE?

I am trying to load data from a text file into a MySQL table, by calling MySQL's LOAD DATA INFILE from a Java process. This file can contain some data for the current date and also for previous days. The table can also contain data for previous dates. The problem is that some of the columns in the file for previous dates might have changed. But I don't want to update all of these columns but only want the latest values for some of the columns.
Example,
Table
+----+-------------+------+------+------+
| id | report_date | val1 | val2 | val3 |
+----+-------------+------+------+------+
| 1 | 2012-12-01 | 10 | 1 | 1 |
| 2 | 2012-12-02 | 20 | 2 | 2 |
| 3 | 2012-12-03 | 30 | 3 | 3 |
+----+-------------+------+------+------+
Data in Input file:
1|2012-12-01|10|1|1
2|2012-12-02|40|4|4
3|2012-12-03|40|4|4
4|2012-12-04|40|4|4
5|2012-12-05|50|5|5
Table after the load should look like
mysql> select * from load_infile_tests;
+----+-------------+------+------+------+
| id | report_date | val1 | val2 | val3 |
+----+-------------+------+------+------+
| 1 | 2012-12-01 | 10 | 1 | 1 |
| 2 | 2012-12-02 | 40 | 4 | 2 |
| 3 | 2012-12-03 | 40 | 4 | 3 |
| 4 | 2012-12-04 | 40 | 4 | 4 |
| 5 | 2012-12-05 | 50 | 5 | 5 |
+----+-------------+------+------+------+
5 rows in set (0.00 sec)
Note that column val3 values are not updated. Also I need to do this for large files as well, some files can be >300Megs or more, and so it needs to be a scalable solution.
Thanks,
Anirudha

It would be good to use LOAD DATA INFILE with REPLACE option, but in this case records will be dropped and added again, so old val3 values will be lost.
Try to load data into temporary table, then update your table from temp. table using INSERT ... SELECT/UPDATE or INSERT ... ON DUPLICATE KEY UPDATE statements.