Dynamic migration dicovery, bug fix (#313)

* Fixes a bug in `get_last_applied_migration` due to an incorrect SQL
  query that partially uses dynamic table names and partially hardcodes
  the default one.

* Adds a new utility function that enables dynamic migration discovery
  where embedding is not desirable.

refinery/src/lib.rs

@@ -32,7 +32,7 @@ for more examples refer to the [examples](https://github.com/rust-db/refinery/tr
 */
 
 pub use refinery_core::config;
-pub use refinery_core::{error, Error, Migration, Report, Runner, Target};
+pub use refinery_core::{error, load_sql_migrations, Error, Migration, Report, Runner, Target};
 #[doc(hidden)]
 pub use refinery_core::{AsyncMigrate, Migrate};
 pub use refinery_macros::embed_migrations;

refinery_core/src/error.rs

@@ -69,6 +69,9 @@ pub enum Kind {
     /// An Error from an underlying database connection Error
     #[error("`{0}`, `{1}`")]
     Connection(String, #[source] Box<dyn std::error::Error + Sync + Send>),
+    /// An Error from an invalid migration file (not UTF-8 etc)
+    #[error("invalid migration file at path {0}, {1}")]
+    InvalidMigrationFile(PathBuf, std::io::Error),
 }
 
 // Helper trait for adding custom messages and applied migrations to Connection error's.

refinery_core/src/lib.rs

@@ -9,7 +9,7 @@ pub use crate::error::Error;
 pub use crate::runner::{Migration, Report, Runner, Target};
 pub use crate::traits::r#async::AsyncMigrate;
 pub use crate::traits::sync::Migrate;
-pub use crate::util::{find_migration_files, MigrationType};
+pub use crate::util::{find_migration_files, load_sql_migrations, MigrationType};
 
 #[cfg(feature = "rusqlite")]
 pub use rusqlite;

refinery_core/src/traits/mod.rs

@@ -115,7 +115,7 @@ pub(crate) const GET_APPLIED_MIGRATIONS_QUERY: &str = "SELECT version, name, app
 
 pub(crate) const GET_LAST_APPLIED_MIGRATION_QUERY: &str =
     "SELECT version, name, applied_on, checksum
-    FROM %MIGRATION_TABLE_NAME% WHERE version=(SELECT MAX(version) from refinery_schema_history)";
+    FROM %MIGRATION_TABLE_NAME% WHERE version=(SELECT MAX(version) from %MIGRATION_TABLE_NAME%)";
 
 pub(crate) const DEFAULT_MIGRATION_TABLE_NAME: &str = "refinery_schema_history";
 

refinery_core/src/util.rs

@@ -1,4 +1,5 @@
 use crate::error::{Error, Kind};
+use crate::Migration;
 use regex::Regex;
 use std::ffi::OsStr;
 use std::path::{Path, PathBuf};
@@ -58,9 +59,41 @@ pub fn find_migration_files(
     Ok(file_paths)
 }
 
+/// Loads SQL migrations from a path. This enables dynamic migration discovery, as opposed to
+/// embedding. The resulting collection is ordered by version.
+pub fn load_sql_migrations(location: impl AsRef<Path>) -> Result<Vec<Migration>, Error> {
+    let migration_files = find_migration_files(location, MigrationType::Sql)?;
+
+    let mut migrations = vec![];
+
+    for path in migration_files {
+        let sql = std::fs::read_to_string(path.as_path()).map_err(|e| {
+            let path = path.to_owned();
+            let kind = match e.kind() {
+                std::io::ErrorKind::NotFound => Kind::InvalidMigrationPath(path, e),
+                _ => Kind::InvalidMigrationFile(path, e),
+            };
+
+            Error::new(kind, None)
+        })?;
+
+        //safe to call unwrap as find_migration_filenames returns canonical paths
+        let filename = path
+            .file_stem()
+            .and_then(|file| file.to_os_string().into_string().ok())
+            .unwrap();
+
+        let migration = Migration::unapplied(&filename, &sql)?;
+        migrations.push(migration);
+    }
+
+    migrations.sort();
+    Ok(migrations)
+}
+
 #[cfg(test)]
 mod tests {
-    use super::{find_migration_files, MigrationType};
+    use super::{find_migration_files, load_sql_migrations, MigrationType};
     use std::fs;
     use std::path::PathBuf;
     use tempfile::TempDir;
@@ -146,4 +179,22 @@ mod tests {
         let mut mods = find_migration_files(migrations_dir, MigrationType::All).unwrap();
         assert!(mods.next().is_none());
     }
+
+    #[test]
+    fn loads_migrations_from_path() {
+        let tmp_dir = TempDir::new().unwrap();
+        let migrations_dir = tmp_dir.path().join("migrations");
+        fs::create_dir(&migrations_dir).unwrap();
+        let sql1 = migrations_dir.join("V1__first.sql");
+        fs::File::create(&sql1).unwrap();
+        let sql2 = migrations_dir.join("V2__second.sql");
+        fs::File::create(&sql2).unwrap();
+        let rs3 = migrations_dir.join("V3__third.rs");
+        fs::File::create(&rs3).unwrap();
+
+        let migrations = load_sql_migrations(migrations_dir).unwrap();
+        assert_eq!(migrations.len(), 2);
+        assert_eq!(&migrations[0].to_string(), "V1__first");
+        assert_eq!(&migrations[1].to_string(), "V2__second");
+    }
 }