build-a-clojure-app-with-cockroachdb.md

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Build a Clojure App with CockroachDB and java.jdbc	Learn how to use CockroachDB from a simple Clojure application with a low-level client driver.	true	false

This tutorial shows you how build a simple Clojure application with CockroachDB using leiningen and the Closure java.jdbc driver.

We have tested the Clojure java.jdbc driver in conjunction with the PostgreSQL JDBC driver enough to claim beta-level support. If you encounter problems, please open an issue with details to help us make progress toward full support.

Before you begin

{% include {{page.version.version}}/app/before-you-begin.md %}

Step 1. Install leiningen

Install the Clojure lein utility as described in its official documentation.

Step 2. Create the maxroach user and bank database

{% include {{page.version.version}}/app/create-maxroach-user-and-bank-database.md %}

Step 3. Generate a certificate for the maxroach user

Create a certificate and key for the maxroach user by running the following command. The code samples will run as this user.

New in v19.1: Pass the --also-generate-pkcs8-key flag to generate a key in PKCS#8 format, which is the standard key encoding format in Java. In this case, the generated PKCS8 key will be named client.maxroach.key.pk8.

{% include copy-clipboard.html %}

$ cockroach cert create-client maxroach --certs-dir=certs --ca-key=my-safe-directory/ca.key --also-generate-pkcs8-key

Step 4. Create a table in the new database

As the maxroach user, use the built-in SQL client to create an accounts table in the new database.

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$ cockroach sql \
--certs-dir=certs \
--database=bank \
--user=maxroach \
-e 'CREATE TABLE accounts (id INT PRIMARY KEY, balance INT)'

Step 5. Run the Clojure code

Now that you have a database and a user, you'll run code to create a table and insert some rows, and then you'll run code to read and update values as an atomic transaction.

Create a basic Clojure/JDBC project

1. Create a new directory myapp.

2. Create a file myapp/project.clj and populate it with the following code, or download it directly.

   {% include copy-clipboard.html %}

   {% include {{ page.version.version }}/app/project.clj %}

3. Create a file myapp/src/test/util.clj and populate it with the code from this file. Be sure to place the file in the subdirectory src/test in your project.

Basic statements

First, use the following code to connect as the maxroach user and execute some basic SQL statements, inserting rows and reading and printing the rows.

Create a file myapp/src/test/test.clj and copy the code below to it, or download it directly. Be sure to rename this file to test.clj in the subdirectory src/test in your project.

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{% include {{ page.version.version }}/app/basic-sample.clj %}

Run with:

{% include copy-clipboard.html %}

$ lein run

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

Copy the code below to myapp/src/test/test.clj or download it directly. Again, preserve the file name test.clj.

{{site.data.alerts.callout_info}} CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code. {{site.data.alerts.end}}

{% include copy-clipboard.html %}

{% include {{ page.version.version }}/app/txn-sample.clj %}

Run with:

{% include copy-clipboard.html %}

$ lein run

After running the code, use the built-in SQL client to verify that funds were transferred from one account to another:

{% include copy-clipboard.html %}

$ cockroach sql --certs-dir=certs -e 'SELECT id, balance FROM accounts' --database=bank

id | balance
+----+---------+
 1 |     900
 2 |     350
(2 rows)

Step 2. Create the maxroach user and bank database

{% include {{page.version.version}}/app/insecure/create-maxroach-user-and-bank-database.md %}

Step 3. Create a table in the new database

As the maxroach user, use the built-in SQL client to create an accounts table in the new database.

{% include copy-clipboard.html %}

$ cockroach sql --insecure \
--database=bank \
--user=maxroach \
-e 'CREATE TABLE accounts (id INT PRIMARY KEY, balance INT)'

Step 4. Run the Clojure code

Now that you have a database and a user, you'll run code to create a table and insert some rows, and then you'll run code to read and update values as an atomic transaction.

Create a basic Clojure/JDBC project

1. Create a new directory myapp.

2. Create a file myapp/project.clj and populate it with the following code, or download it directly.

   {% include copy-clipboard.html %}

   {% include {{ page.version.version }}/app/project.clj %}

3. Create a file myapp/src/test/util.clj and populate it with the code from this file. Be sure to place the file in the subdirectory src/test in your project.

Basic statements

First, use the following code to connect as the maxroach user and execute some basic SQL statements, inserting rows and reading and printing the rows.

Create a file myapp/src/test/test.clj and copy the code below to it, or download it directly. Be sure to rename this file to test.clj in the subdirectory src/test in your project.

{% include copy-clipboard.html %}

{% include {{ page.version.version }}/app/insecure/basic-sample.clj %}

Run with:

{% include copy-clipboard.html %}

$ lein run

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

Copy the code below to myapp/src/test/test.clj or download it directly. Again, preserve the file name test.clj.

{{site.data.alerts.callout_info}} CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code. {{site.data.alerts.end}}

{% include copy-clipboard.html %}

{% include {{ page.version.version }}/app/insecure/txn-sample.clj %}

Run with:

{% include copy-clipboard.html %}

$ lein run

After running the code, use the built-in SQL client to verify that funds were transferred from one account to another:

{% include copy-clipboard.html %}

$ cockroach sql --insecure -e 'SELECT id, balance FROM accounts' --database=bank

id | balance
+----+---------+
 1 |     900
 2 |     350
(2 rows)

What's next?

Read more about using the Clojure java.jdbc driver.

{% include {{ page.version.version }}/app/see-also-links.md %}