I need to fetch all tables in a particular Postgres database using node. But not finding any way to achieve that. Is there any way to get that?
For example, suppose I have a database named 'TestDatabase' it contains 4 tables( just assume it can have less or more) Person, Company, Clothes, Animal.
I need to get the name of all of them using node.
I am also using node-postgres ('pg') to connect with the database.
As an alternative you can use information_schema. It is not better then the pg_* objects in the system catalog but is standardized and more portable. Here it is:
select table_schema||'.'||table_name as table_fullname
from information_schema."tables"
where table_type = 'BASE TABLE'
and table_schema not in ('pg_catalog', 'information_schema');
The system objects have been filtered by this expression
table_schema not in ('pg_catalog', 'information_schema')
You can further modify it to only include schemas that you need.
This is a generic solution. Use the query below:
SELECT
relname
FROM
pg_class
WHERE
relkind = 'r';
pg_class is the system catalog that holds information on table like objects. Hence the need to restrict relkind to 'r'. This will include all table types. To further restrict see relpersistence at link below.
https://www.postgresql.org/docs/current/catalog-pg-class.html
Related
Looking at the following lines of code:
query = "DROP TABLE IF EXISTS my_table"
cur.execute(query)
conn.commit()
# print(table_name)
I'm running the query against multiple tables with various query and I want to return the name of the table and the action executed each time. Is there a way to get some kind of meta data from cur.execute or conn.commit on the action running?
In the example above I'd like to print the table name (my_table) and the action (DROP TABLE). however I want this to be dynamic. If I'm creating a table I want to the name of the table newly created and the action (CREATE TABLE).
Thanks.
Quick and Dirty
tables = ['table_1', 'table_2', 'table_3']
action = 'DROP TABLE'
for table in tables:
cur.execute(f'{str(action)} IF EXISTS {str(table)}')
print(f'ACTION: {action}')
print(f'TABLE: {table}')
conn.commit()
HOWEVER, please do not ever do something like this in anything other than a tiny app that will never leave your computer, and especially not with anything that will accept input from a user.
Bad things will happen.
Dynamically interfacing with databases using OOP is a solved problem, and its not worth reinventing the wheel. Have you considered using an ORM like SQLAlchemy?
I would like to do more complex queries on jsonb/documents that contain arrays of objects. Is there any library anyone would recommend for Node? I am using pg but I want to do more advanced queries like select the document where a document has an array with an object with a certain key/value. If there aren't any libraries that do this, does anyone know how I could do it with json functions/etc in psql? or point me to a book/resource where I could learn this advanced querying?
If you need to do really complicated things you're going to be writing SQL no matter what. But for basic queries that involve working with JSONB fields Massive (full disclosure, it's my project) has you covered, and executing handwritten prepared statements is as easy as anything else since scripts are loaded into the API.
Searching an embedded array falls into the 'really complicated' category, unfortunately, but if you know your element positions you could do this quite simply with Massive:
await db.mytable.find({
'somejson.arrayfield[0].key': 'value'
});
This would return all records from mytable where the somejson column has an arrayfield array, the first element in which contains a "key": "value" pair.
For searching, check out the Postgres docs. The specific question you have requires a lateral join on the jsonb_array_elements function like so:
SELECT somejson
FROM mytable
JOIN LATERAL jsonb_array_elements(mytable.somejson->'arrayfield') AS elements
ON TRUE
WHERE elements->>'key' = $1;
With Massive, you'd put this query in a script in your application's /db directory and run it as db.myScriptName('value'). You can use folders to group similar scripts too.
My question is pretty simple. I am working on Kentico 9 with its SQL Server database which contains several tables which had been added directly from the SQL Management Studio by an external contractor. The fact is that those tables are being used to store custom content which will be displayed for a site, but, in the code they don't have the code for making queries. I mean, they don't have Info and Provider classes.
https://docs.kentico.com/display/K82/Retrieving+database+data+using+ObjectQuery+API
According with this, all tables into the Kentico database can be accessed by invoking methods on these classes, but I don't have it this time.
Something like this, it will not work if I use my table name:
var user = UserInfoProvider.GetUserInfo("administrator");
var items = CustomTableItemProvider.GetItems("MyTable")
.TopN(10)
.WhereEquals("ItemCreatedBy", user.UserID)
.OrderBy("ItemCreatedWhen");
My question is:
can I query any table by its name?
One last thing:
I cannot declared those table as "custom table" because it seems to be a bug in the CMS.
Or you can pull data using your own SQL query:
var ds = ConnectionHelper.ExecuteQuery("select ....", null, QueryTypeEnum.SQLQuery);
Nevertheless I would recommend to create a custom class inside a custom module (much more robust than custom tables) instead and use the generated Info and InfoProvider classes to get and manipulate data.
I think an object has to be registered within the system (created through Kentico UI or API) in order to be pulled from DB with object query.
So I'd choose one of the following options:
Use Entity Framework or something similar to work with that data
Create appropriate custom tables or even custom module and push data there. Not sure why you can't create a custom table... What is an error you're getting?
If you need to present data on the UI only (without processing on the back end) - use just custom queries
Hope this helps.
If you are accessing in code then you could do it the good old fashioned way. If you want to pull data from the database to display on the website you could also do so by creating a custom query and using a transformation to display the fields, then use a repeater on the page to display the transformed data. Alternatively you can use a SQL datasource with a basic repeater, but you still have to create a transformation to display the data. Both methods allow you to access the data in the tables from within the CMS UI, no need to touch any code behind.
If your objective is to read data from these database tables to transform on webpage e.g. using CMS Repeater webpart, you can simply create custom query(s) in Kentico itself and load data using it. You can find the detail here on how to create custom custom queries and load data using it.
On the other hand you can also write your custom classes and define the custom methods where you can pull data using your own SQL query like this:
var ds = ConnectionHelper.ExecuteQuery("select ....", null, QueryTypeEnum.SQLQuery);
Lastly I don't think there should be any issue to create custom table instead of those direct DB tables, only thing we have to ensure code name of custom table should be unique means don't try to use exact same name because it'll cause exception due to same table name already exist in DB. You can please share exception you getting while creating custom table so that I can help you out further.
I have found out that SubSonic SimpleRepository expectes plural table names however I have started working on a database that doesn't have this and I am unable to change the table names.
Is there a way I can use Subsonic without making database changes?
I have seen one suggestion but I don't fancy that too much.
I'm not tied to using the SimpleRepository I just thought it would be easiest as I need the ability to swap database connections (SQL & Oracle) based on the clients requirements. The schema is the same on both. With SimpleRepository I can just swap out the connection string in the web.config.
You can apply the SubSonicTableNameOverride attribute on your classes you use with Simple Repo and use an arbitrary table name!
I am using subsonic simplerepo with migrations in dev and it makes things pretty easy but I keep running into issues with my nvarchar columns that have an index. My users table has an index defined on the username column for obvious reasons but each time I start the project subsonic is doing this:
ALTER TABLE [Users] ALTER COLUMN Username nvarchar(50);
which causes this:
The index 'IX_Username' is dependent on column 'Username'.ALTER TABLE ALTER COLUMN Username failed because one or more objects access this column
Is there any way around this issue?
Which DBMS are you using? Sql Server?
Never had a problem like this with MySQL, but it seems that your DBMS does not allow to alter a column with an index on it. This is not a SubSonic related issue.
Maybe you should do:
Execute("DROP index ...");
AlterColumn("...");
Execute("CREATE index ...");
It is one or the other. If you choose to manage your DB by Subsonic (use migrations), you can't use indexes and stuff. Sorry mate.