如何在 GET 请求中从 mongodb 过滤和 select 特定字段？

Question

I have just started working with mongoose/mongodb and node.js to build the backend of a react native app I am working on. I'm getting fairly comfortable with querying documents in the database from node but how do I set those "filters" in a GET request (using fetch) from the front end?

If a user applies a filter to a list to only return products of a certain price, how do I get that filter from the client side over to the server side so node can make the proper query on the database?

Same question for if I only want to return specific fields as opposed to returning every field in a mongodb document. How can I let the backend know what fields to return from the client side?

Hopefully that all makes sense, like I said I'm very new to both mongo and node so I apologize if my explanations are not the best.

Thank you to anyone who can help!

Answer 1

What you're looking for is a query language - a syntax for conveying the parameters of a query to a server. There are several options.

Some sites decide to only support simple queries. The simplest query language, in this case, is the GET query string. For instance, if you're building an on-line store, your customers will typically need to search for products by name and by category, and so you may end up with two query string parameters that you support in URLs, like this:
/products?category=clothes&search=t-shirt

Then, your application must process each of these parameters independently - your back-end must know how to turn this into a MongoDB query. For example:

products.find({
  category: { $eq: req.query.category },
  $text: { $search: req.query.search }
  // similarly, you could accept params such as "pricemin" and "pricemax"
  //  and construct a { $gt, $lt } query
});

For more complex systems or applications that require more flexibility, you can allow the client to construct a complete query on their own and pass that to the back-end for evaluation. Multiple solutions exist that let you achieve this - GraphQL is a popular choice lately due to its good tooling support and ease of use. Another well-known solution is OData, which is used in some high-profile APIs, such as Microsoft Graph API .

If using an advanced query language, your back-end will always need to translate between the format that's sent to the server and the format that the database speaks. The simplest, non-generic example is the code snippet above - though batteries-included solutions will normally come with their own translators, so you may not need to write any code yourself if a package exists that does that for you.