I am using Hibernate 3.3.1 and PostgresQL 9.2.2 server. The tables for my application
are generated by hibernate automatically and now i would like to do an optimization for
a very often used "like" expression in a table wich looks that wy:
"where path like 'RootFolder_FirstSubfolder%'"
by default hibernate only creates an index for the "id" column i defined via annotation.
Are there any recommendations how i could speedup my "like" expression using more indexes?
Thanks very much in advance for helping me
Kind regards
Shannon
Hibernate can use the Index annotation to automatically creating an additional index:
#org.hibernate.annotations.Index(name = "IDX_PATH")
private String path;
BUT it won't help since the created index is not suitable for like clauses.
Read the most upvoted answer here for a better solution. Unfortunately, it requires custom sql and AFAIK there is no easy way to integrate custom sql in script generated by hibernate schema update tool.
As an alternative to hibernate auto update: you can use a tool like liquibase to manage schema update. It requires more setup, but it gives you full control of schema update scripts.
Related
PostgreSQL has excellent support for evaluating JSONPath expressions against JSON data.
For example, this query returns true because the value of the nested field is indeed "foo".
select '{"header": {"nested": "foo"}}'::jsonb #? '$.header ? (#.nested == "foo")'
Notably this query does not reference any schemas or tables. Ideally, I would like to use this functionality of PostgreSQL without creating or connecting to a full database instance. Is it possible to run PostgreSQL in such a way that it doesn't have schemas or tables, but is still able to evaluate "standalone" queries?
Some other context on the project, we need to evaluate JSONPath expressions against JSON data in both a Postgres database and Python application. Unfortunately, Python does not have any JSONPath libraries that support enough of the spec to be useful to us.
Ideally, I would like to use this functionality of PostgreSQL without creating or connecting to a full database instance.
Well, it is open source. You can always pull out the source code for this functionality you want and adapt it to compile by itself. But that seems like a large and annoying undertaking, and I probably wouldn't do it. And short of that, no.
Why do you need this? Are you worried about scalability or ease of installation or performance or what? If you are already using PostgreSQL anyway, firing up a dummy connection to just fire some queries at the JSONB engine doesn't seem too hard.
SQLAlchemy 1.4 ORM using an AsyncSession, Postgres backend, Python 3.6
I am trying to create a custom aggregate function using the SQLAlchemy ORM. The SQL query would look something like:
COUNT({group_by_function}),{group_by_function} AS {aggregated_field_name)}
I've been searching for information on this.
I know this can be created internally within the Postgres db first, and then used by SA, but this will be problematic for the way the codebase I'm working with is set up.
I know SQLAlchemy-Utils has functionality for this, but I would prefer not to use an external library.
The most direct post on this topic I can find says "The creation of new aggregate functions is backend-dependant, and must be done directly with the API of the underlining connection." But this is from quite a few years ago and thought there might have been updates since.
Am I missing something in the SA ORM docs that discusses this or is this not supported by SA, full stop?
you can try something this query
query = db.session.query(Model)\
.with_entities(
Model.id,
func.sum(Model.number).label('total_sum')
).group_by(Model.id)
I have a sequence created using flyway in postgres which should start from 10000.
I want to get the next value of the sequence using JPA and not a native query , since i have different db platforms being run at different cloud providers.
I'm not able to find a JPA query to get the next value of a sequence, please redirect me to the right page if i am missing something already ..
Thanks for any help in that area though already!
P.S : I found this link which helps me doing the same with native query.
postgresql sequence nextval in schema
I don't think this is possible in a direct way.
JPA doesn't know about sequences.
Only the implementation knows about those and utilizes them to create ids.
I see the following options to get it to work anyway:
create a view in the database with a single row and a single column containing the next value. You can query that with native SQL which should be the same for all databases since it is a trivial select.
Create a dummy entity using the sequence for id generation, save a new instance and let JPA populate the id.
A horrible workaround but pure JPA.
Bite the bullet and create a simple class that provides the correct native SQL statement to use for the current environment and execute it via JdbcTemplate.
As part of some requirement, I need to migrate a schema from some existing database to a new schema in a different database. Some part of it is already done and now I need to compare the 2 schema and make changes in the new schema as per gap finding.
I am not using a tool and was trying to understand some details using syscat command but could not get much success.
Any pointer on what is the best way to solve this?
Regards,
Ramakant
A tool really is the best way to solve this – IBM Data Studio is free and can compare schemas between databases.
Assuming you are using DB2 for Linux/UNIX/Windows, you can do a rudimentary compare by looking at selected columns in SYSCAT.TABLES and SYSCAT.COLUMNS (for table definitions), and SYSCAT.INDEXES (for indexes). Exporting this data to files and using diff may be the easiest method. However, doing this for more complex structures (tables with range or database partitioning, foreign keys, etc) will become very complex very quickly as this information is spread across a lot of different system catalog tables.
An alternative method would be to extract DDL using the db2look utility. However, you can't specify the order that db2look outputs objects (db2look extracts DDL based on the objects' CREATE_TIME), so you can't extract DDL for an entire schema into a file and expect to use diff to compare. You would need to extract DDL into a separate file for each table.
Use SchemaCrawler for IBM DB2, a free open-source tool that is designed to produce text output that is designed to be diffed. You can get very detailed information about your schema, including view and stored procedure definitions. All of the information that you need will be output in a single file, and can be compared very easily using a standard diff tool.
Sualeh Fatehi, SchemaCrawler
unfortunately as per company policy, cannot use these tools at this point of time. So am writing some program using JDBC to get the details and do some comparison kind of stuff.
Is there a simple way of doing this in doctrine, or am I going to have to do a native sql query? If someone could point me in the right direction, it would be appreciated.
Quick answer is, no. There is not a "simple way" of doing this.
You need to use Doctrine Native SQL which can be found here. This will allow you to map the results into usable entities like you're used to while using database specific things.
You could also use a DQL user defined function, described here. This is probably the "correct" way.