I would like to ask for suggestions from all of you guys, which is the best choice to fetch data with ONE TO MANY relationship using Spring JDBC? I decide to use Spring JDBC because I have a complex query.
Ex: I have two tables which are student and subject. A student can study many subjects. So, I will join these tables using one-to-many relationships.
Join level DB: I can join on the level database but I need to map on level by code using loop then add subjects as a list of student objects.
Call separate query, One for student and using student_id to find in subjects table
what do you think, please give me the advice?
Thank you!
Related
I just start to learning DynamoDB and I face a big problem.
Suppose, I have an author and a book table where the author can have multiple books and each book must have an author.
so, In NonSQL DB I just embedded author information in book table to solve this problem.
Sample code: https://pastebin.ubuntu.com/p/DvHpS8JQJV/
But, recently I face a problem which is, if long time later admin want to change some information about author like, live attribute. How can I make effect in book table.
Note: Embedded book collection in author table could solve this problem but in future retrieve all books data with pagination and other operation could be more difficult.
In relational db it's every easy to solve just use foreign key and retrieve data by using join query.
How can I solve this type of problem In NonSQL or dynamoDB any suggestions?
You have two options.
Go with semi-sql design. Create separate table for books and autor. And joins will be handled on application level. It's not perfect from performance perspective, but it's easy to start for devs with SQL background.
Go with single table design. This is a complex topic. There is no silver bullet to handle one-to-many relationships like in SQL. You need good understanding of your domain and single table design to do this well.
Using mongodb and waterline, how can I query a collection taking in count a relationship with other?
For example, let's say I have two collections, Employer and Employee. An employer can have one or more employees. How could I get a list of employers based in a property of an employee, like getting the list of employers that have employees with an age above of 25 years.
I know that could be done with two queries specifying the required parameters, but I wonder if that could be done in one query, like mysql using joins.
Thanks for your time.
No. MongoDB does not support joins so if you need if your data is not embedded in a single collection you will need to use two queries to achieve the result you want
I want to make a one to one relationship between two tables.How to do this?I've read documentation but there is only some examples.I think i should do something on schema.Thanks for help
I have the following objects Company, User and Order (contains orderlines). User's place orders with 1 or more orderlines and these relate to a Company. The time period for which orders can be placed for this Company is only a week.
What I'm not sure on is where to place the orders array, should it be a collection of it's own containing a link to the User and a link to the Company or should it sit under the Company or finally should the orders be sat under the User.
Numbers wise I need to plan for 50k+ in orders.
Queries wise, I'll probably be looking at Orders by Company mainly but I would need to find an Order by Company based for a specific user.
1) For folks coming from the SQL world (such as myself) one of the hardest learn about MongoDB is the new style of schema design. In the SQL world, everything goes into third normal form. Folks come to think that there is a single right way to design their schema, because there typically is one.
In the MongoDB world, there is no one best schema design. More accurately, in MongoDB schema design depends on how the application is going to access the data.
2) Here are the key questions that you need to have answered in order to design a good schema for MongoDB:
How much data do you have?
What are your most common operations? Will you be mostly inserting new data, updating existing data, or doing queries?
What are your most common queries?
How many I/O operations do you expect per second?
What you're talking about here is modeling Many-to-One relationships:
Company -> User
User -> Order
Order -> Order Lines
Company -> Order
Using SQL you would create a pair of master/detail tables with a primary key/foreign key relationship. In MongoDB, you have a number of choices: you can embed the data, you can create a linked relationship, you can duplicate and denormalize the data, or you can use a hybrid approach.
The correct approach would depend on a lot of details about the use case of your application, many of which you haven't provided.
3) This is my best guess - and it's only a guess - as to a good schema for you.
a) Have separate collections for Users, Companies, and Orders
If you're looking at 50k+ orders, there are too many to embed in a single document. Having them as a separate collection will allow you to reference them from both the Company and the User documents.
b) Have an array of references to the Order documents in both the Company and the User documents. This makes the query "Find all Orders for this Company" a single-document query
c) If your query pattern supports it, you might also have a duplicate link from Orders back to the owning Company and/or User.
d) Assuming that the order lines are unique to the individual Order, you would embed the Order Lines in an array within the Order documents.
e) If your order lines refer back to individual Products, you might want to have a separate Product collection, and include a reference to the Product document in the order line sub-document
4) Here are some good general references on MongoDB schema design.
MongoDB presentations:
http://www.10gen.com/presentations/mongosf2011/schemabasics
http://www.10gen.com/presentations/mongosv-2011/schema-design-by-example
http://www.10gen.com/presentations/mongosf2011/schemascale
Here are a couple of books about MongoDB schema design that I think you would find useful:
http://www.manning.com/banker/ (MongoDB in Action)
http://shop.oreilly.com/product/0636920018391.do
Here are some sample schema designs:
http://docs.mongodb.org/manual/use-cases/
Note that the "MongoDB in Action" book includes a sample schema for an e-commerce application, which is very similar to what you're trying to build -- I recommend you check it out.
At my company we have a database with one table being so big that it was splitted into 3 tables. They all share an ID and the info is NOT normalized so there is info for several entities in the tables, some entities actually have some fields in one table and some fields in the other tables.
There is a new project and they want to use nHibernate to map it, so that the code uses the ORM and we work on objects rather than query strings.
One of the problems we are having is that we are using nHibernates fluent "join" to map the 3 tables into one, but nHibernate won't let you map components inside joins, also it seems liek you cant map components that are split several tables.
Is Entity Framework 4 capable of doing this?
Yes. So does EF 1. It's called entity splitting.