Add Run SQL Script Against Postgres Container as a Docker TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1622 TILs and counting..._
+_1623 TILs and counting..._
 
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@@ -230,6 +230,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [List Running Docker Containers](docker/list-running-docker-containers.md)
 - [Prevent Containers From Running On Startup](docker/prevent-containers-from-running-on-startup.md)
 - [Run A Basic PostgreSQL Server In Docker](docker/run-a-basic-postgresql-server-in-docker.md)
+- [Run SQL Script Against Postgres Container](docker/run-sql-script-against-postgres-container.md)
 
 ### Drizzle
 

docker/run-sql-script-against-postgres-container.md

@@ -0,0 +1,42 @@
+# Run SQL Script Against Postgres Container
+
+I've been using dockerized Postgres for local development with several projects
+lately. This is typically with framework tooling (like Rails) where schema
+migrations and query execution are handled by the tooling using the specified
+connection parameters.
+
+However, I was experimenting with and iterating on some Postgres functions
+outside of any framework tooling. I needed a way to run the SQL script that
+(re)creates the function via `psql` on the docker container.
+
+With a local, non-containerized Postgres instance, I'd redirect the file to
+`psql` like so:
+
+```bash
+$ psql -U postgres -d postgres < experimental-functions.sql
+```
+
+When I tried doing this with `docker exec` though, it was silently failing /
+doing nothing. As far as I can tell, there was a mismatch with redirection
+handling across the bounds of the container.
+
+To get around this, I first copy the file into the `/tmp` directory on the
+container:
+
+```bash
+$ docker cp experimental-functions.sql still-postgres-1:/tmp/experimental-functions.sql
+```
+
+Then the `psql` command that docker executes can be pointed directly at a
+local-to-it SQL file.
+
+```bash
+$ docker exec still-postgres-1 psql \
+  -U postgres \
+  -d postgres \
+  -f /tmp/experimental-functions.sql
+```
+
+There are probably other ways to handle this, but I got into a nice rhythm with
+this file full of `create or replace function ...` definitions where I could
+modify, copy over, execute, run some SQL to verify, and repeat.