We Keep Coding

h2 database and sql server in spring boot

I was asked this question by a colleague, and I am unable to answer it:
I have an in memory database (h2), and I have a SQL database server which our app needs to talk too. But due to the two different SQL dialects we are now wondering how do we get around the issue by doing the least amount of work?
This to be done in spring boot. I am aware of how to connect to the h2 database and SQL database server, but I am unsure on the rest.

If everything is setup by Spring, you should not be worried about the 2 different SQL dialects. Just be sure that spring.jpa.database is set to default to let Spring autodetect the right dialect for each datasource.
Here's a link that explain how to use/initialize two datasource in a Spring Boot projet if you need some more information.

spring boot sql database DML and DDL scripts

How i could define some schema and data to be inserted into db for
sql database in spring boot
Also could i do this for embedded databases
For example i am using two databases and i want to populate some data or define some schema and apply to different databases before application starts.

A file named import.sql in the root of the classpath is executed on startup if Hibernate creates the schema from scratch (that is, if the ddl-auto property is set to create or create-drop). This can be useful for demos and for testing if you are careful but is probably not something you want to be on the classpath in production. It is a Hibernate feature (and has nothing to do with Spring).
You can take a look in spring docs

Spring Boot schema.sql - drop db schema on restart

Hi I'm using Spring Boot version 1.5.9.
When using Spring Boot to initialize schema.sql for mysql database, it works all fine and the database schema is getting created successfully. But on restart of the application this schema.sql script is executing again and the application fails to start because the tables already exist.
I tried spring.jpa.hibernate.ddl-auto=create-drop option in application.properties but it does not have any effect (probably because it only works for Hibernate entities which I'm not using)
Is there a way to have Spring Boot to re-create schema from schema.sql every time on restart if the database is not in-memory one?
GitHub:
https://github.com/itisha/spring-batch-demo/tree/database-input

According to the documentation you can simply ignore exceptions by setting spring.datasource.continue-on-error property to true
Spring Boot enables the fail-fast feature of the Spring JDBC
initializer by default, so if the scripts cause exceptions the
application will fail to start. You can tune that using
spring.datasource.continue-on-error.
or even turn it off with spring.datasource.initialize set to false
You can also disable initialization by setting spring.datasource.initialize to false.

A workaround could be, to change the create statements in your schema.sql
from
CREATE TABLE test .....
to
CREATE TABLE IF NOT EXISTS test ...
use the IF NOT EXISTS statements

turn off automatic schema creation to avoid conflicts: add this line in your application.properties
spring.jpa.hibernate.ddl-auto=none

How to execute sql script after db schema generation but before application startup

I want to generate DB structure from my Java classes
jpa.generate-ddl: true
jpa.ddl-auto: true
Also, I need to run SQL script before application will up because I have #PostConstruct methods where I use these data.
Can you show an example how to do it in Spring Boot?

A simple spring boot app with the required functionality can be found at.
https://github.com/salilotr89/Spring-boot-postgres-dbinit
Spring JDBC has a DataSource initializer feature. Spring Boot enables it by default and loads SQL from the standard locations schema.sql and data.sql (in the root of the classpath).
In addition Spring Boot will load the schema-${platform}.sql and data-${platform}.sql files (if present), where platform is the value of spring.datasource.platform, e.g. you might choose to set it to the vendor name of the database (hsqldb, h2, oracle, mysql, postgresql etc.).
Spring Boot enables the fail-fast feature of the Spring JDBC initializer by default, so if the scripts cause exceptions the application will fail to start. The script locations can be changed by setting spring.datasource.schema and spring.datasource.data, and neither location will be processed if spring.datasource.initialize=false.
To disable the fail-fast you can set spring.datasource.continue-on-error=true. This can be useful once an application has matured and been deployed a few times, since the scripts can act as ‘poor man’s migrations’ — inserts that fail mean that the data is already there, so there would be no need to prevent the application from running, for instance.
If you want to use the schema.sql initialization in a JPA app (with Hibernate) then ddl-auto=create-drop will lead to errors if Hibernate tries to create the same tables. To avoid those errors set ddl-auto explicitly to "" (preferable) or "none". Whether or not you use ddl-auto=create-drop you can always use data.sql to initialize new data.
http://docs.spring.io/spring-boot/docs/current/reference/html/howto-database-initialization.html
For Reference: Spring Boot - Loading Initial Data

Hibernate database name change gives MySQLSyntaxErrorException: Table doesn't exist

I used to have a database called database and everything was working well using hibernate and its models.
I removed <property name="hibernate.hbm2ddl.auto"> to avoid update or create as it's a production server, we want to do it manually.
We recently switched to database2 and so we switched the hibernate configuration file and all the hibernate XML models.
`<class name="com.api.models.database.MmApplications" table="mm_applications" catalog="database2">`
but it keeps looking for database event if we migrated the database, the models and the connexion.
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'database.mm_applications' doesn't exist
Does someone can help me ?
UPDATE ----
Hibernate is connecting to the right database (database2), but there is a prefix as a prefix database. making the queries hitting the database instead of database2, and when I try to force the default_schema my queries become :
`... from database.database2.mm_applications ....`
Any idea?

My database is specified in the hibernate.connection.url property. Have you changed that also ? An example would be: jdbc:mysql://localhost/mydatabase
Also, instead of removing hibernate.hbm2ddl.auto then perhaps you should set its value to validate. That way hibernate will ensure that the datamodel matches the database schema.

I found the problem, It was an other application deployed on the same tomcat server using hibernate as well with another database (database) making a conflict with the new application ...
There is still something weird, by connecting to any database, hibernate will use the specified catalog in the hibernate models and so constructing the request using the catalog.table_name
Hope this help someone someday.