I am new to linq query and EFCore, I am needed to design an API which updates multiple rows of data. This is an example of my current database table in postgresql:
| id | value |
| ---- | ----- |
| 1 | 123 |
| 2 | 456 |
I want to write an update API using linq query to allow user to update using JSON into:
| id | value |
| ---- | ----- |
| 1 | abc |
| 2 | zxc |
What is the best approach to code this API?
My advice is you try to use the out-of-the-box functionality. So do the changes you want to do, and then when you are happy do the SaveChanges() that does everything.
And then ask about specific challenges you experience.
Related
Background:
I'm working on a project that does not allow me to share the data, but I'll do my best to give you some visualisation below. So before going further, I know (some) SQL, and I have done basic work relationship before, but the data was clean and simple and for some reason I just can't' figure out a solution.
Problem (?)
I'm trying to define a relationship between two tables from two different sources that each work with different identifiers. I do have however a mapping table from one of those but again the identifiers do not align. Let me try explain visually:
| TABLE 1 (cies) | | TABLE 2 (forms) |
| ------------ | | ------------- |
| id(PK) | | id(PK) |
| 4_digit_code | | 16_digit_code |
| ...more fields | | ...more fields |
The second source provided me a mapping table they use internally:
| MAPPING TABLE |
| ------------- |
| id(PK) |
| 4_digit_code | (= to the one in TABLE 1)
| 16_digit_code | (= to the one in TABLE 2)
My first thought was to create a script and just merge the info in the mapping table in TABLE 1 like so:
| TABLE 1 | | TABLE 2 |
| ------------ | | ------------- |
| id(PK) | | id(PK) |
| 16_digit_code | ==== | 16_digit_code |
| 4_digit_code |
The issue here is the 16_digit_code is not unique so I believe this does not work. Now comes something I have no experience with so I am just thinking out loud here:
Can I keep (?) the mapping table and each time reference that one to get my data from the other table via another? On other hand should not all values in a mapping table be unique as well for it to work? The reason there are non-unique values is that (some) very old numbers end up getting recycled.
For example get me all forms from company with id 1:
| TABLE 1 | | MAPPING TABLE | | TABLE 2 |
| ------------ | | ------------- | | ------------- |
| id(PK) | | id(PK) | | id(PK) |
| 16_digit_code | | 16_digit_code | ==== | 16_digit_code |
| 4_digit_code | ==== | 4_digit_code | | ...more fields |
And in the above, I would not know how to efficiently approach this problem. I really don't know if it makes any sense though what I am saying or I am missing something or making this way too complex.
Solution?
I'd love it if someone could point me in the right direction. And if you have the solution I'd love to know the reasoning, not just the solution as I'd love to learn from this for the future obviously.
Edit/Clarification:
Just for completion sake, the mapping combination (4 digit + 16 digit code) is unique. Although, as I said earlier one 16 digit code can be linked to multiple 4 digit codes.
Sorry, I'm very new to SQL. I just learned it few hours ago. I'm using MariaDB + InnoDB Engine with HeidiSQL software + CodeIgniter 3. Let's say I have a table named disciples with the following data:
-------------------
| sort_id | name |
-------------------
| 1 | Peter |
| 4 | John |
| 3 | David |
| 5 | Petrus |
| 2 | Matthew |
-------------------
I'm fully aware that it's better to have a column called sort_id to be able to fetch the data using ORDER BY if I prefer a custom sorting. But if I delete row 3, the new table will look like this:
-------------------
| sort_id | name |
-------------------
| 1 | Peter |
| 4 | John |
| 5 | Petrus |
| 2 | Matthew |
-------------------
The thing is I'm having OCD (imagine there are 1000 rows), it hurts my eyes to see this mess with some missing numbers (in this case number 3 - see the above table) under sort_id. I think it has something to do with "relational database". Is there a way to quickly and automatically "re-assign/reset" new sort_id numbers to given rows and sort them ASC order according to the name using SQL code without having to do it manually?
-------------------
| sort_id | name |
-------------------
| 1 | John |
| 2 | Matthew |
| 3 | Peter |
| 4 | Petrus |
-------------------
I figured this out after reading the answer from Lynn Crumbling.
She made me realized I need a primary key in order to have a better management for my rows which is exactly what I was looking for. It happens that InnoDB automatically creates a primary key and is hidden from HeidiSQL interface unless I specify a specific column for example id. Now, I can re-organize my table rows by editing the primary key id and the table row will automatically sort itself the way I want. Before this, I edited the sort_id but the data did not update accordingly because it was not the primary key.
------------------------
| id | sort_id | name |
------------------------
| 1 | 1 | Peter |
| 2 | 4 | John |
| 3 | 5 | Petrus |
| 4 | 2 | Matthew |
------------------------
Thank you.
I have a table that contains the history of Customer IDs that have been merged in our CRM system. The data in the historical reporting Oracle schema exists as it was when the interaction records were created. I need a way to find the Current ID associated with a customer from potentially an old ID. To make this a bit more interesting, I do not have permissions to create PL/SQL for this, I can only create Select statements against this data.
Sample Data in customer ID_MERGE_HIST table
| OLD_ID | NEW_ID |
+----------+----------+
| 44678368 | 47306920 |
| 47306920 | 48352231 |
| 48352231 | 48780326 |
| 48780326 | 50044190 |
Sample Interaction table
| INTERACTION_ID | CUST_ID |
+----------------+----------+
| 1 | 44678368 |
| 2 | 48352231 |
| 3 | 80044190 |
I would like a query with a recursive sub-query to provide a result set that looks like this:
| INTERACTION_ID | CUST_ID | CUR_CUST_ID |
+----------------+----------+-------------+
| 1 | 44678368 | 50044190 |
| 2 | 48352231 | 50044190 |
| 3 | 80044190 | 80044190 |
Note: Cust_ID 80044190 has never been merged, so does not appear in the ID_MERGE_HIST table.
Any help would be greatly appreciated.
You can look at CONNECT BY construction.
Also, you might want to play with recursive WITH (one of the descriptions: http://gennick.com/database/understanding-the-with-clause). CONNECT BY is better, but ORACLE specific.
If this is frequent request, you may want to store first/last cust_id for all related records.
First cust_id - will be static, but will require 2 hops to get to the current one
Last cust_id - will give you result immediately, but require an update for the whole tree with every new record
I have a table to store reservations for certain events; relevant part of it is:
class Reservation(models.Model):
# django creates an auto-increment field "id" by default
event = models.ForeignKey(Event)
# Some other reservation-specific fields..
first_name = models.CharField(max_length=255)
Now, I wish to retrieve the sequential ID of a given reservation relative to reservations for the same event.
Disclaimer: Of course, we assume reservations are never deleted, or their relative position might change.
Example:
+----+-------+------------+--------+
| ID | Event | First name | Rel.ID |
+----+-------+------------+--------+
| 1 | 1 | AAA | 1 |
| 2 | 1 | BBB | 2 |
| 3 | 2 | CCC | 1 |
| 4 | 2 | DDD | 2 |
| 5 | 1 | EEE | 3 |
| 6 | 3 | FFF | 1 |
| 7 | 1 | GGG | 4 |
| 8 | 1 | HHH | 5 |
+----+-------+------------+--------+
The last column is the "Relative ID", that is, a sequential number, with no gaps, for all reservations of the same event.
Now, what's the best way to accomplish this, without having to manually calculate relative id for each import (I don't like that)? I'm using postgresql as underlying database, but I'd prefer to stick with django abstraction layer in order to keep this portable (i.e. no database-specific solutions, such as triggers etc.).
Filtering using Reservation.objects.filter(event_id = some_event_id) should suffice. This will give you a QuerySet that should have the same ordering each time. Or am I missing something in your question?
I hate always being the one that responds its own questions, but I solved using this:
class Reservation(models.Model):
# ...
def relative_id(self):
return self.id - Reservation.objects.filter(id__lt=self.id).filter(~Q(event=self.event)).all().count()
Assuming records from reservations are never deleted, we can safely assume the "relative id" is the incremental id - (count of reservations before this one not belonging to same event).
I'm thinking of any drawbacks, but I didn't find any.
I'm sure this has been asked but I can't quite find the right search terms.
Given a schema like this:
| CarMakeID | CarMake
------------------------
| 1 | SuperCars
| 2 | MehCars
| CarMakeID | CarModelID | CarModel
-----------------------------------------
| 1 | 1 | Zoom
| 2 | 1 | Wow
| 3 | 1 | Awesome
| 4 | 2 | Mediocrity
| 5 | 2 | YoureSettling
I want to produce a dataset like this:
| CarMakeID | CarMake | CarModels
---------------------------------------------
| 1 | SuperCars | Zoom, Wow, Awesome
| 2 | MehCars | Mediocrity, YoureSettling
What do I do in place of 'AGG' for strings in SQL Server in the following style query?
SELECT *,
(SELECT AGG(CarModel)
FROM CarModels model
WHERE model.CarMakeID = make.CarMakeID
GROUP BY make.CarMakeID) as CarMakes
FROM CarMakes make
http://www.simple-talk.com/sql/t-sql-programming/concatenating-row-values-in-transact-sql/
It is an interesting problem in Transact SQL, for which there are a number of solutions and considerable debate. How do you go about producing a summary result in which a distinguishing column from each row in each particular category is listed in a 'aggregate' column? A simple, and intuitive way of displaying data is surprisingly difficult to achieve. Anith Sen gives a summary of different ways, and offers words of caution over the one you choose...
If it is SQL Server 2017 or SQL Server VNext, Azure SQL database you can use String_agg as below:
SELECT make.CarMakeId, make.CarMake,
CarModels = string_agg(model.CarModel, ', ')
FROM CarModels model
INNER JOIN CarMakes make
ON model.CarMakeId = make.CarMakeId
GROUP BY make.CarMakeId, make.CarMake
Output:
+-----------+-----------+---------------------------+
| CarMakeId | CarMake | CarModels |
+-----------+-----------+---------------------------+
| 1 | SuperCars | Zoom, Wow, Awesome |
| 2 | MehCars | Mediocrity, YoureSettling |
+-----------+-----------+---------------------------+