Start adding more migrations

pg-worm/src/migration/mod.rs

@@ -57,6 +57,46 @@ impl Table {
 
         self
     }
+
+    fn up(&self) -> String {
+        let mut up = format!(
+            "CREATE TABLE {} ({})",
+            self.name,
+            self.columns.iter().map(|i| i.up())._join(", ")
+        );
+
+        if !self.constraints.is_empty() {
+            up.push_str(&format!(
+                ", {}",
+                self.constraints.iter().map(|i| i.up())._join(", ")
+            ));
+        }
+
+        up
+    }
+
+    fn down(&self) -> String {
+        format!("DROP TABLE IF EXISTS {}", self.name)
+    }
+
+    fn drop_all_constraints_cascading(&self) -> String {
+        // This is a pl/pgsql code block which first queries for all
+        // constraints on a given table and then removes them.
+        format!(
+            r#"DO $$
+                DECLARE i RECORD;
+                BEGIN
+                    FOR i IN (SELECT conname
+                        FROM pg_catalog.pg_constraint con
+                        INNER JOIN pg_catalog.pg_class rel ON rel.oid = con.conrelid
+                        INNER JOIN pg_catalog.pg_namespace nsp ON nsp.oid = connamespace
+                        WHERE rel.relname = {0}) LOOP
+                    EXECUTE format('ALTER TABLE {0} DROP CONSTRAINT %I CASCADE', i.conname);
+                END LOOP;
+            END $$;"#,
+            self.name
+        )
+    }
 }
 
 impl Column {
@@ -98,32 +138,7 @@ impl Column {
 
         self
     }
-}
-
-trait Up {
-    fn up(&self) -> String;
-}
-
-impl Up for Table {
-    fn up(&self) -> String {
-        let mut up = format!(
-            "CREATE TABLE {} ({})",
-            self.name,
-            self.columns.iter().map(|i| i.up())._join(", ")
-        );
-
-        if !self.constraints.is_empty() {
-            up.push_str(&format!(
-                ", {}",
-                self.constraints.iter().map(|i| i.up())._join(", ")
-            ));
-        }
-
-        up
-    }
-}
 
-impl Up for Column {
     fn up(&self) -> String {
         let mut up = format!("{} {}", self.name, self.data_type);
 
@@ -141,9 +156,40 @@ impl Up for Column {
 
         up
     }
+
+    fn down(&self) -> String {
+        format!("DROP COLUMN IF EXISTS {}", self.name)
+    }
+
+    fn migrate_from(&self, other: &Column, table: &Table) -> Vec<String> {
+        let mut statements = Vec::new();
+
+        if other.constraints.len() > 0 {
+            statements.push(table.drop_all_constraints_cascading());
+        }
+
+        if self.constraints.len() > 0 {
+            let mut stmts = self
+                .constraints
+                .iter()
+                .map(|i| i.migrate_to(&self))
+                .collect::<Vec<String>>();
+
+            statements.append(&mut stmts);
+        }
+
+        if self.data_type != other.data_type {
+            statements.push(format!(
+                "ALTER COLUMN {} SET TYPE {}",
+                self.name, self.data_type
+            ));
+        }
+
+        statements
+    }
 }
 
-impl Up for TableConstraint {
+impl TableConstraint {
     fn up(&self) -> String {
         use TableConstraint as C;
 
@@ -167,7 +213,7 @@ impl Up for TableConstraint {
     }
 }
 
-impl Up for ColumnConstraint {
+impl ColumnConstraint {
     fn up(&self) -> String {
         use ColumnConstraint as C;
 
@@ -184,8 +230,21 @@ impl Up for ColumnConstraint {
             C::RawCheckNamed(name, check) => format!("CONSTRAINT {name} CHECK ({check})"),
         }
     }
+
+    fn migrate_to(&self, column: &Column) -> String {
+        use ColumnConstraint as C;
+
+        match self {
+            C::NotNull => format!("ALTER COLUMN {} DROP NULL", column.name),
+            C::PrimaryKey => format!("ADD CONSTRAINT PRIMARY KEY ({})", column.name),
+            C::Unique => format!("ALTER COLUMN {} SET UNIQUE", column.name),
+            _ => todo!(),
+        }
+    }
 }
 
+/// Convenience method to avoid writing `.iter().map(|i| i.to_string()).collect::<Vec<String>>().join()`
+/// all the time.
 trait Join {
     fn _join(self, _: &str) -> String;
 }
@@ -206,8 +265,6 @@ where
 
 #[cfg(test)]
 mod tests {
-    use crate::migration::Up;
-
     use super::{Column, Table};
 
     #[test]