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For this guide, we're going to walk through some simple examples foreach of the pieces of CRUD, which stands for 'Create Read UpdateDelete'. Each step in this guide will build on the previous, and ismeant to be followed along.
This guide assumes that you're using PostgreSQL. Before we start,make sure you have PostgreSQL installed and running.
Diesel requires Rust 1.24 or later. If you're followingalong with this guide, make sure you're using at least thatversion of Rust by running rustup update stable.
The first thing we need to do is generate our project.
First, let's add Diesel to our dependencies. We're also going to use atool called .env to manage our environment variablesfor us. We'll add it to our dependencies as well.
Diesel provides a separate CLI tool to help manage yourproject. Since it's a standalone binary, and doesn't affect yourproject's code directly, we don't add it to Cargo.toml. Instead, wejust install it on our system.
diesel_cliIf you run into an error like:
This means you are missing the client library needed for adatabase backend – mysqlclient in this case. You can resolvethis issue by either installing the library (using the usual wayto do this depending on your operating system) or by excluding theundesired default library with the --no-default-features flag.
For example, if you only have PostgreSQL installed, you can usethis to install diesel_cli with only PostgreSQL:
We need to tell Diesel where to find our database. We do this bysetting the DATABASE_URL environment variable. On our developmentmachines, we'll likely have multiple projects going, and we don't wantto pollute our environment. We can put the url in a .env fileinstead.
Now Diesel CLI can set everything up for us.
This will create our database (if it didn't already exist), and createan empty migrations directory that we can use to manage our schema(more on that later).
Now we're going to write a small CLI that lets us manage a blog(ignoring the fact that we can only access the database from thisCLI…). The first thing we're going to need is a table to store ourposts. Let's create a migration for that:
Diesel CLI will create two empty files for us in the required structure.You'll see output that looks something like this:
Migrations allow us to evolve the database schema over time. Eachmigration can be applied (up.sql) or reverted (down.sql). Applyingand immediately reverting a migration should leave your database schemaunchanged.
Next, we'll write the SQL for migrations:
We can apply our new migration:
It's a good idea to make sure that down.sql is correct. You can quickly confirmthat your down.sql rolls back your migration correctly by redoing the migration:
Since migrations are written in raw SQL, they can contain specificfeatures of the database system you use. For example, theCREATE TABLE statement above uses PostgreSQL's SERIAL type.If you want to use SQLite instead, you need to use INTEGERinstead.
When preparing your app for use in production, you may want to run your migrations duringthe application's initialization phase. You may also want to include the migration scriptsas a part of your code, to avoid having to copy them to your deployment location/image etc.
The diesel_migrations crate provides the embed_migrations! macro, allowing you to embedmigration scripts in the final binary. Once your code uses it, you can simply include embedded_migrations::run(&db_conn)at the start of your main function to run migrations every time the application starts.
OK enough SQL, let's write some Rust. We'll start by writing some codeto show the last five published posts. The first thing we need to do isestablish a database connection.
We'll also want to create a Post struct into which we can read ourdata, and have diesel generate the names we'll use to reference tablesand columns in our queries.
We'll add the following lines to the top of src/lib.rs:
Next we need to create the two modules that we just declared.
#[derive(Queryable)] will generate all of the code needed toload a Post struct from a SQL query.
Typically the schema module isn't created by hand,it gets generated by Diesel.When we ran diesel setup,a file called diesel.toml was createdwhich tells Diesel to maintain a file at src/schema.rs for us.The file should look like this:
The exact output might vary slightly depending on your database,but it should be equivalent.
The table! macro creates a bunch of code based on the database schemato represent all of the tables and columns. We'll see howexactly to use that in the next example.
Any time we run or revert a migration, this file will get automatically updated.
Using #[derive(Queryable)] assumes that the order of fields on thePost struct matches the columns in the posts table, so makesure to define them in the order seen in the schema.rs file.
Let's write the code to actually show us our posts.
The use posts::dsl::* line imports a bunch of aliases so that we cansay posts instead of posts::table, and published instead ofposts::published. It's useful when we're only dealing with a singletable, but that's not always what we want.
We can run our script with cargo run --bin show_posts. Unfortunately,the results won't be terribly interesting, as we don't actually haveany posts in the database. Still, we've written a decent amount ofcode, so let's commit.
The full code for the demo at this point can be foundhere.
Next, let's write some code to create a new post. We'll want a structto use for inserting a new record.
Now let's add a function to save a new post.
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When we call .get_result on an insert or update statement, itautomatically adds RETURNING * to the end of the query, and lets usload it into any struct that implements Queryable for the righttypes. Neat!
Diesel can insert more than one record in a single query. Just pass aVec or slice to insert, and then call get_results instead ofget_result. If you don't actually want to do anything with the rowthat was just inserted, call .execute instead. The compiler won'tcomplain at you, that way. :)
Now that we've got everything set up, we can create a little script towrite a new post.
We can run our new script with cargo run --bin write_post. Go aheadand write a blog post. Get creative! Here was mine:
Unfortunately, running show_posts still won't display our new post,because we saved it as a draft. If we look back to the code inshow_posts, we added .filter(published.eq(true)), and we hadpublished default to false in our migration. We need to publish it!But in order to do that, we'll need to look at how to update anexisting record. First, let's commit. The code for this demo at thispoint can be found here.
Now that we've got create and read out of the way, update is actuallyrelatively simple. Let's jump right into the script:
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That's it! Let's try it out with cargo run --bin publish_post 1.
And now, finally, we can see our post with cargo run --bin show_posts.
We've still only covered three of the four letters of CRUD though. Let's showhow to delete things. Sometimes we write something we really hate, andwe don't have time to look up the ID. So let's delete based on thetitle, or even just some words in the title.
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We can run the script with cargo run --bin delete_post demo (at leastwith the title I chose). Everyday i love you download. Your output should look something like:
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When we try to run cargo run --bin show_posts again, we can see thatthe post was in fact deleted. This barely scratches the surface of whatyou can do with Diesel, but hopefully this tutorial has given you agood foundation to build off of. We recommend exploring the APIdocs to see more. The final code for this tutorial can be foundhere.