I am trying to understand that how object initialization works for returned object by Session Get method.Please validate my understanding. When it executes, it checks for object with given identifier in the first level cache and then the Second level cache (If it is configured), If not found then fires the select query to retrieve the data from database.
My question is, Does it include associations in select query which are configured for lazy loading or null value is set for such associations in returned object?
If this is case then session.get does not do the complete initialization of the returned object which is contradictory to what is written on most of hibernate tutorials available on web.
Hibernate Session provide different methods to fetch data from database. Two of them are – get() and load().
get() returns the object by fetching it from database or from hibernate cache.
when we use get() to retrieve data that doesn’t exists, it returns null, because it try to load the data as soon as it’s called.
We should use get() when we want to make sure data exists in the database.
For Example :
In a Stock application , Stock and StockTransactions should have a “one-to-many” relationship, when you want to save a stock transaction, it’s common to declared something like below.
Stock stock = (Stock)session.get(Stock.class, new Integer(2));
StockTransaction stockTransactions = new StockTransaction();
//set stockTransactions detail
stockTransactions.setStock(stock);
session.save(stockTransactions);
Output :
Hibernate:
select ... from mkyong.stock stock0_
where stock0_.STOCK_ID=?
Hibernate:
insert into mkyong.stock_transaction (...)
values (?, ?, ?, ?, ?, ?)
In session.get(), Hibernate will hit the database to retrieve the Stock object and put it as a reference to StockTransaction.
To answer the question:
Does it include associations in select query which are configured for lazy loading or null value is set for such associations in returned object?
1) The session.get() will NOT initiate lazy stuff. NEVER. In fact that is the central thought of the design. Otherwise - we would be able to load whole DB in one SHOT (in one JAVA call to session.get())
2) And also there WILL NOT be null instead. Each reference or collection will be represented by proxy. This is the way how we can avoid to load compelte DB in one shot (all stuff initialized with one method get). Because each proxy is in fact a promise - once we will touch it... it will load the real data.
And so on. So get is very safe way how to recieve as few data as was configured....
Simply
When get() method is called, it will directly hit the database, fetch the result and return. If no matching fields are found, it will gladly return null.
Depending on the annotations on references, Lazy or Eager, data will be returned. if Lazy, proxy will be returned instead of null, if Eager, fully initialized object will be returned.
Better to monitor the queries at the backend, for good understanding.
1) Customer entity class that map the T_CUSTOMER DB table:
#Entity
#Table(name= “T_CUSTOMER”)
public class Customer {
#Id
#Column (name=“cust_id”)
private Long id;
#OneToMany(fetch=FetchType.EAGER)
#JoinColumn (name=“cid”)
private Set<Address> addresses;
…
…
…
}
2) Address entity class that map the T_ADDRESS DB table:
#Entity
#Table(name= “T_ADDRESS”)
public class Address {
// Fields and Properties
}
Consider this Customers table :
----------------------------------------------------------------------------
| Cust_id | Cust_firstname | Cust_lastname | Cust_email | Cust_mobile |
----------------------------------------------------------------------------
| 101 | XXXX | YYYYY |xxx#xyz.com | 8282263131 |
----------------------------------------------------------------------------
The Above customers table is having one record with cust_id as 101.
Now Consider this Address Table :
----------------------------------------------------------------------------
| id | street | suburb | city | zipcode | cid |
----------------------------------------------------------------------------
| 1 | streetX | AreaY | cityZ | 54726 | 101 |
----------------------------------------------------------------------------
| 2 | streetXA | AreaYB | cityZS | 60660 | 101 |
----------------------------------------------------------------------------
Now When you invoke :
Customer cust = (Customer)session.get(Customer.class, 101);
Then Hibernate will fire a SQL Query Something like :
1). In case of EAGER LOADING :
SELECT * FROM T_CUSTOMER cust JOIN T_ADDRESS add ON cust.cust_id=add.cid
i.e, It will load all the data related to the T_CUSTOMERS table and it's associated tables, which is T_ADDRESS table in this case.
2). I case of LAZY LOADING :
SELECT * FROM T_CUSTOMER WHERE cust_id=101;
So, it only fetches the data corresponding to the T_CUSTOMER table and uses Proxy for the T_ADDRESS table as said above by #Radim Köhler. It will fetch the data from the T_ADDRESS TABLE only when you'll call :
cust.getAddresses();
Related
I have two tables (Leave, CompOff) I want to show these tables data to user(frontend) in form of Requests from employee. Employee can request for leave and compoff. Both the tables have createdOn, empid column. And I am not understanding how to fetch both table data and then return a list which contain both the tables data.
Leave tables -
empid | ceated_on
1 | 09-07-2022
2 | 05-07-2022
3 | 02-07-2022
CompOff tables -
empid | ceated_on
1 | 08-07-2022
2 | 06-07-2022
3 | 01-07-2022
In Springboot I have created three classes name - leave, compoff, request. And they have some create/update opertaion. Now in request class I want both (leave,compoff) data and send to user.
Use a union not a join.
Create a native query something like:
select 'leave' as type, empid, created_on, <other columns>
from leave
union all
select 'compoff', empid, created_on, <same other columns as above>
from compoff
I have the following schema and I am not sure how to model it in Firestore.
I will be having clients and invoices. Clients "has" invoices. I need to be able to do these 2 queries:
Show invoices that a client has
Update all invoices in the system (change a boolean attribute from true to false).
What would be the right way to model this? The first query is satisfied by having a collection of clients with subcollection of their invoices. But the second one is satisfied by having a collection of all invoices?
Any experienced help is appreciated
Thank you
I have another recommendation which involves you to create two top level collections like this:
Firestore-root
|
--- users (collection)
| |
| --- userId (documents)
| |
| --- //user details
|
--- invoices (collection)
|
--- invoiceId (documents)
|
--- yourBooleanProperty: true
|
--- userId: true
As you can see, the simplest way to achieve this, is to have a single collection named invoices that can hold as documents all the invoices in your database. Because a single invoice can belong only to a single user, you can have the userId as a property. To get all the invoices that correspond to a specific user, I recommend you to use the following query:
FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
Query query = rootRef.collection("invoices").whereEqualTo(userId, true);
And if you want to change the boolean property of all invoices from true to false at once, simply use the following query:
Query query = rootRef.collection("invoices").whereEqualTo(yourBooleanProperty, true);
Remember that Firestore uses a document-oriented NoSQL model, similar to MongoDB and CouchDB, which leads to fundamentally different data structuring decisions.
You can think this structure in a relational way, and you can achieve the same results.
And you already did that here
The first query is satisfied by having a collection of clients with
subcollection of their invoices.
so in order to solve your last requirement i would make a collection with all the invoices and then share with the clients invoice the current invoice id, so you will have inside your first query a subcollection with the ids to refer to your all invoices, this way you can refer to them and make any changes you want just querying the first collection.
let me just illustrates how they can connect
In my application each user can have multiple authorization roles. Depending on his roles the user should be allowed to see certain excerpts of data. I want to provide this data from my relational database via a REST-API.
For example:
table "Role"
UserName | Role
---------------------------
Anne | ViewFreshFruits
Mike | ViewFreshFruits
Mike | ViewTinySoft
table "Company"
Name | Address | Role
--------------------------------------------
FreshFruits | 123 America | ViewFreshFruits
TinySoft | 543 Britain | ViewTinySoft
table "Contract"
ID | CompanyName | Dollar
---------------------------
147 | FreshFruits | 15549
148 | FreshFruits | 16321
149 | TinySoft | 2311
To implement the REST-Resource http://api:8080/Application/Contracts/getAll the data (without permission check) could simply be:
SELECT Contract.* FROM Contract
But Anne is only allowed to see 147 and 148. Mike can see 147, 148, 149. And Tomy must not get any results.
I started to implement the permission check like this:
SELECT Contract.* FROM Contract
INNER JOIN Company ON Contract.CompanyName = Company.Name
INNER JOIN Role ON Role.Role = Company.Role
WHERE User = #CurrentlyAuthenticatedUser
This kind of SQL gains complexity with the number of tables in my database. I'm looking for an easier approach: less complex and easier to maintain. Performance is not my primary concern.
How can I filter certain rows of data, depending on the user, as simple as possible?
I'm using a Microsoft SQL Server 2012, Java Tomcat 8 and Connection Pooling.
That seems the easiest way to create and maintain.
If you want to have a faster SQL query, that doesn't need joins, you could create a materialized view based on that query, but without the WHERE clause and with the User on the column selection.
SELECT User, Contract.* FROM Contract
INNER JOIN Company ON Contract.CompanyName = Company.Name
INNER JOIN Role ON Role.Role = Company.Role
That way you would have a virtual table that keeps that query saved and up to date for fast authentication data retrieval. To select you would only need to:
SELECT * FROM MaterializedView
WHERE User = #CurrentlyAuthenticatedUser
How about stored procedures where you pass the role. Or to simplify you select use a view to hide some of the details.
edit
Create a view on company and authorisation tables (or a stored procedure or CTE)
CREATE VIEW CompanySecurity AS SELECT Company.*, role.username FROM Company INNER JOIN Role ON Role.Role = Company.Role
If you want contract details join that view to CompanySecurity and filter on username
If you want to see Sales, join sales to CompanySecurity and filter on username
I would like to know how to create custom setups/teardown mostly to fix cyclyc refence issues where I can insert custom SQL commands with Spring Test Dbunit http://springtestdbunit.github.io/spring-test-dbunit/index.html.
Is there an annotation I can use or how can this be customized?
There isn't currently an annotation that you can use but you might be able to create a subclass of DbUnitTestExecutionListener and add custom logic in the beforeTestMethod. Alternatively you might get away with creating your own TestExecutionListener and just ordering it before DbUnitTestExecutionListener.
Another, potentially better solution would be to re-design your database to remove the cycle. You could probably drop the reference from company to company_config and add a unique index to company_id in the company_config table:
+------------+ 1 0..1 +--------------------------------+
| company |<---------| company_config |
+------------+ +--------------------------------+
| company_id | | config_id |
| ... | | company_id (fk, notnull, uniq) |
+------------+ +--------------------------------+
Rather than looking at company.config_id to get the config you would do select * from company_config where company_id = :id.
Dbunit needs the insert statements (xml lines) in order, because they are performed sequentially. There is no or magic parameter or annotation so dbunit can resolve your cyclyc refences or foreign keys automatically.
The most automate way I could achieve if you your data set contain many tables with foreign keys:
Populate your database with few records. In your example: Company, CompanyConfig and make it sure that the foreign keys are met.
Extract a sample of your database using dbunit Export tool.
This is an snippets you could use:
IDatabaseConnection connection = new DatabaseConnection(conn, schema);
configConnection((DatabaseConnection) connection);
// dependent tables database export: export table X and all tables that have a // PK which is a FK on X, in the right order for insertion
String[] depTableNames = TablesDependencyHelper.getAllDependentTables(connection, "company");
IDataSet depDataset = connection.createDataSet(depTableNames);
FlatXmlWriter datasetWriter = new FlatXmlWriter(new FileOutputStream("target/dependents.xml"));
datasetWriter.write(depDataset);
After running this code, you will have your dbunit data set in "dependents.xml", with all your cycle references fixed.
Here I pasted you the full code: also have a look on dbunit doc about how to export data.
We have the following (poorly designed?) table:
inputs:
keyword_id serial not null,
group_name string not null,
banned_term string not null
Keyword ID is the primary key. there are many banned terms per group_name. The data looks like this:
keyword_id | group_name | banned_term
1 | incentivization | free money
2 | inaccuracy | we're number one
3 | incentivization | win a free ipod!
There's no join table, and group_name isn't its own entity. I'd like a domain object something like this:
class BannedTermGroup {
Integer id;
String group_name;
Set<String> banned_terms;
// ... various getters and setters
}
The only examples on this one-to-many relationship between the group name and banned terms all involve some sort of join column or join table, while group_name would always be part of some other entity. Here neither is the case. Can this be mapped using Hibernate?
As quoted in my previous comment, you can get the ID of the group from nowhere.
Just to put aside this problem, you may look into Hibernate's reference, search for collections of basic types. It is what you need.
However, you still need to have a table for the "group".
assume it is as simple as a one column table:
KEYWORD_GROUP
--------------------
GROUP_NAME STRING
Your original keyword table:
KEYWORD
--------------------
GROUP_NAME STRING
KEYWORD STRING
I believe this is what you need:
#Entity
#Table("KEYWORD_GROUP")
public class KeywordGroup {
[.....]
#ElementCollection
#CollectionTable(name="KEYWORD", joinColumns=#JoinColumn(name="GROUP_NAME"))
#Column(name="KEYWORD")
private List<String> keywords;
}
For the keyword_group table, you probably don't need to create a new table if you are just using this model for read. Create a view from your original keyword table should be good enough.