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34 lines
1.1 KiB
Markdown
34 lines
1.1 KiB
Markdown
# Check If User Role Exists For Database
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User roles define who can access a database cluster and broadly what level of
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control they have over that cluster.
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The most straightforward way to check if a user role exists is to connect to
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one of the databases in the cluster and run a query against the `pg_roles`
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table.
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```sql
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select * from pg_roles where rolename='dev';
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rolname
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------------
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dev
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(1 row)
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```
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This same concept can be used in a script when automating some database setup.
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To do that, we'll use `-c` (and some other flags) to dispatch a query to `psql`
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from a shell context.
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```bash
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psql postgres -tXAc "SELECT 1 FROM pg_roles WHERE rolname='dev'" \
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| grep -q 1 \
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|| createuser --interactive dev
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```
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This queries for the value `1` if the user role named `dev` exists. The output
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of that is piped to `grep` (in quiet mode, `-q`) to check if `1` is in the
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output. If user roles doesn't exist and grep doesn't match on `1`, then the
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right side of the _or_ (`||`) gets called. That command could be whatever. I've
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chosen to call PostgreSQL's `createuser` to create the `dev` user role.
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