I am trying to use Gorm as ORM with MySQL 8.0.22 for data type JSON. Does GORM support this to bind to the struct?
You can try the helper datatypes package https://github.com/go-gorm/datatypes, which contains a JSON type that is compatible with MySQL, among other databases.
Related
Is there a way to use SQL Server table-valued parameters in Entity Framework in a way that doesn't require you to use a stored procedure or string-based queries like context.Database.ExecuteSqlCommandAsync("") ?
Something similar to Dapper where I can pass a DataTable and specify the user-defined type name to use. Probably must be some sort of overload of IEnumerable<>.Contains() or .Join() so that I can build a join in a generated query.
The goal is to stay with expression trees and don't mess with strings.
Is there an easy way to determine or find the underlying SQL field type of a Django Field, for any of the supported by default database backends? I have searched on the web and there is no documentation over how the Django fields are represented in SQL in each of the supported databases. The only way for me to see the underlying SQL field type, is to run the mysqlmigrate command of manage.py and examine the SQL code.
The type depends on the database backend, so you need to get a db connection first:
from django.db import connection
and now you can look up the field via the model Meta API:
my_field = MyModel._meta.get_field('my_field_name')
and use its db_type method:
my_field.db_type(connection)
which will return something like "varchar(10)".
Be sure you really need to do this, though. Usually this information is only useful inside migrations.
I can not find proper documentation of SQEUENCE object used in SQL Loader. Can someone please refer to me to a proper use of SEQUENCE object. How does it get its value. where does it persist etc.
How SEQUENCE (MAX, 1) in SQL LOADER is different from My_Seq.nextval in oracle client ?
Direct load does not allow the My_Seq.nextval entity, however, as you've indicated, the SEQUENCE(max,1) construct can be used. The documentation is found in the utilities reference:
https://docs.oracle.com/database/121/SUTIL/toc.htm
I have a function which maps java to SQL types.
As I want to store binary data, is there any type defined by the SQL standard which I can use both in PostgreSQL and hsqldb?
The SQL 92 standard does not define a binary type. PostgreSQL has a bytea type, hsqldb has a binary type.
For a very portable (if not efficient) solution, convert the binary to base64, and store it in a string.
BINARY and VARBINARY are defined by the the SQL Standard. The Standard is currently at SQL:2011 (after 92, 1999, 2003 and 2008). HSQLDB supports all the core data types defined by the Standard.
The PostgreSQL BYTEA is similar to VARBINARY. You can define the BYTEA type in HSQLDB as a VARBINARY type with a large maximum size:
CREATE TYPE BYTEA AS VARBINARY(1000000)
SQL has supported binary types since 1999: [https://mariadb.com/kb/en/sql-data-types/]. Vendors have had over a decade to add support for binary types, and most SQL databases do.
If there are 2 columns in database, eg.
code varchar(3)
name nvarchar(50)
How to tell hibernate to pass varchar for searching by code?
In the hibernate mappings string is mapped to nvarchar and it produces queries like:
Select code, name From table where code=N'AAA' (instead of code='AAA')
This is very bad as it causes index scan instead of index seek operation (scanning all index nodes instead of directly going to requested one)
As code is used in millions of rows as well as in several indexes and foreign keys, changing it from varchar to nvarchar will cause performance degradation (more IO operations as nvarchar uses twice more space than varchar).
Is there any way to tell hibernate to do mapping according to database type, not to Java type?
Thanks
Probably you already solved this, but I had a similar problem.
I'm using jTDS JDBC driver and I solved the index scan problem by adding:
;sendStringParametersAsUnicode=false;prepareSQL=0
to the end of the jTDS connection string.
Probably it would not had solved your problem because by doing this, jTDS will only use VARCHAR (no NVARCHAR anymore).
Also, I had to disable the prepared SQL, because Hibernate is using 'like' instead of '=' when generating the queries and by using 'like' combined with a variable (SELECT ... WHERE column LIKE #var) causes an index scan (MSSQL 2000).
I'm assuming you're talking about NHibernate rather than Hibernate because the latter does not use nvarchar in its default SqlServer dialect.
The way to solve your problem is to specify column type as "AnsiString" in your mapping:
<property name="Code" type="AnsiString"/>
Take a look at this post for more details.
<type-mapping>
<sql-type jdbc-type="NVARCHAR" hibernate-type="string" />
</type-mapping>
Add the above code in the hibernate reveng file.
In hibernate.properties set the property hibernate.connection.defaultNChar=false.
You can either hide your tables behind views or use nstring type. This type is available in hibernate-core 4.x. In hibernate-core 3.6.10.Final you will need to define the custom type nstring - see the comment in the url:
Getting Hibernate and SQL Server to play nice with VARCHAR and NVARCHAR.