(feature): add org-roam-db-location (#350)

`org-roam-db-location` sets the location of the Org-roam sqlite database.

CHANGELOG.md

@@ -1,11 +1,16 @@
 # Changelog
 
+## 1.0.1 (TBD)
+
+### New Features
+* [#350][gh-350] Add `org-roam-db-location`
+
 ## 1.0.0 (23-03-2020)
 
 Org-roam is now on MELPA! We have squashed most of the bugs, and Org-roam has
 been stable for the most part.
 
-## New Features
+### New Features
 * [#269][gh-269] Add `org-roam-graphviz-extra-options`
 * [#257][gh-257] Add a company-backend `company-org-roam`
 * [#284][gh-284], [#289][gh-289] Configurable `org-roam-completion-system` with options `'default`, `'ido`, `'ivy` and `'helm`
@@ -13,7 +18,7 @@ been stable for the most part.
 * [#290][gh-290] Add `org-roam-date-title-format` and `org-roam-date-filename-format` for customizing Org-roam's date files
 * [#296][gh-296] Allow multiple exclusion matchers in `org-roam-graph-exclude-matcher`
 
-## Bugfixes
+### Bugfixes
 * [#293][gh-293] Fix capture templates not working as expected for `org-roam-find-file`
 * [#275][gh-275] Fix database rebuild when `org-roam-directory` is set locally
 
@@ -148,6 +153,7 @@ Mostly a documentation/cleanup release.
 [gh-290]: https://github.com/jethrokuan/org-roam/pull/290
 [gh-293]: https://github.com/jethrokuan/org-roam/pull/293
 [gh-296]: https://github.com/jethrokuan/org-roam/pull/296
+[gh-350]: https://github.com/jethrokuan/org-roam/pull/350
 
  # Local Variables:
  # eval: (auto-fill-mode -1)

org-roam.el

@@ -131,8 +131,14 @@ Formatter may be a function that takes title as its only argument."
 
 ;;; Database
 ;;;; Options
-(defconst org-roam-db-filename "org-roam.db"
-  "Name of the Org-roam database file.")
+(defcustom org-roam-db-location nil
+  "Location of the Org-roam database.
+If this is non-nil, the Org-roam sqlite database is saved here.
+
+It is the user's responsibility to set this correctly, especially
+when used with multiple Org-roam instances."
+  :type 'string
+  :group 'org-roam)
 
 (defconst org-roam--db-version 1)
 (defconst org-roam--sqlite-available-p
@@ -147,7 +153,8 @@ Formatter may be a function that takes title as its only argument."
 (defun org-roam--get-db ()
   "Return the sqlite db file."
   (interactive "P")
-  (expand-file-name org-roam-db-filename org-roam-directory))
+  (or org-roam-db-location
+      (expand-file-name "org-roam.db" org-roam-directory)))
 
 (defun org-roam--get-db-connection ()
   "Return the database connection, if any."