Introduce model.Transaction()

It is a very common pattern that some function needs to access the
database and wants to wrap all the actions into one transaction.

The advantage of a transaction is that it is ACID:

- atomic
- consistent
- isolated
- durable

In Go it is required to request a new transaction, execute functionality
on it and handle rollback or commit of this transaction based on the
success of the operation.

All this and the error handling can be written down in the
model.Transaction() function exactly once. The full signature of it is:

	func Transaction(f func(*sql.Tx) error) error

It requires a function or closure passed as argument which takes the
transaction (*sql.Tx) and returns an error which might be nil.

This is very generic. It is applied to:

- injecting test data
- database migrations
- data read requests
- data write requests

1 files changed, 62 insertions, 67 deletions

diff --git a/model/recipe_test.go b/model/recipe_test.go
index 7b6c14c..74ccfa2 100644
--- a/model/recipe_test.go
+++ b/model/recipe_test.go
@@ -1,11 +1,12 @@
 package model
 
 import (
+	"database/sql"
+	"fmt"
+	"os"
+	"path/filepath"
 	"reflect"
 	"testing"
-	"path/filepath"
-	"os"
-	"fmt"
 )
 
 func TestRecipeCrud(t *testing.T) {
@@ -25,68 +26,62 @@ func TestRecipeCrud(t *testing.T) {
 	InitDatabase(filepath.Join(storage.Path, "ceres.sqlite3"))
 	defer CloseDatabase()
 
-	tx, err := NewTx()
-	if err != nil {
-		t.Fatalf("Failed to inject test recipes: %v\n", err)
-	}
-
-	var original, readback, update, updated, deleted Recipe
-
-	recipes := RecipeTestData()
-	original = recipes[0]
-	update = recipes[1]
-
-	err = original.Create(tx)
-	if err != nil {
-		t.Fatalf("Failed to create test recipe in DB: %v\n", err)
-	}
-
-	readback.Id = original.Id
-	err = readback.Read(tx)
-	if err != nil {
-		t.Fatalf("Failed to read test recipe from DB: %v\n", err)
-	}
-
-	if !reflect.DeepEqual(original, readback) {
-		t.Fatalf("Recipes did not match after create / read cycle:\n"+
-			"Before: %s\nAfter: %s\n", original, readback)
-	}
-
-	update.Id = original.Id
-
-	err = update.Update(tx)
-	if err != nil {
-		t.Fatalf("Failed to update recipe: %v\n", err)
-	}
-
-	updated.Id = original.Id
-	err = updated.Read(tx)
-	if err != nil {
-		t.Fatalf("Failed to read back updated recipe: %v\n", err)
-	}
-
-	if !reflect.DeepEqual(update, updated) {
-		t.Fatalf("Recipes did not match after update / read cycle:\n"+
-			"Update: %s\nUpdated: %s\n", update, updated)
-	}
-
-	if reflect.DeepEqual(updated, original) {
-		t.Fatalf("Updated and original recipe match")
-	}
-
-	err = updated.Delete(tx)
-	if err != nil {
-		t.Fatalf("Failed to delete updated recipe: %v\n", err)
-	}
-
-	deleted.Id = updated.Id
-	err = deleted.Read(tx)
-	if err == nil {
-		t.Fatalf("Was able to read back deleted recipe")
-	}
-
-	err = tx.Commit()
-	if err != nil {
-		t.Fatalf("Unable to commit test transaction")
-	}
+	Transaction(func(tx *sql.Tx) error {
+		var original, readback, update, updated, deleted Recipe
+
+		recipes := RecipeTestData()
+		original = recipes[0]
+		update = recipes[1]
+
+		err = original.Create(tx)
+		if err != nil {
+			t.Fatalf("Failed to create test recipe in DB: %v\n", err)
+		}
+
+		readback.Id = original.Id
+		err = readback.Read(tx)
+		if err != nil {
+			t.Fatalf("Failed to read test recipe from DB: %v\n", err)
+		}
+
+		if !reflect.DeepEqual(original, readback) {
+			t.Fatalf("Recipes did not match after create / read cycle:\n"+
+				"Before: %s\nAfter: %s\n", original, readback)
+		}
+
+		update.Id = original.Id
+
+		err = update.Update(tx)
+		if err != nil {
+			t.Fatalf("Failed to update recipe: %v\n", err)
+		}
+
+		updated.Id = original.Id
+		err = updated.Read(tx)
+		if err != nil {
+			t.Fatalf("Failed to read back updated recipe: %v\n", err)
+		}
+
+		if !reflect.DeepEqual(update, updated) {
+			t.Fatalf("Recipes did not match after update / read cycle:\n"+
+				"Update: %s\nUpdated: %s\n", update, updated)
+		}
+
+		if reflect.DeepEqual(updated, original) {
+			t.Fatalf("Updated and original recipe match")
+		}
+
+		err = updated.Delete(tx)
+		if err != nil {
+			t.Fatalf("Failed to delete updated recipe: %v\n", err)
+		}
+
+		deleted.Id = updated.Id
+		err = deleted.Read(tx)
+		if err == nil {
+			t.Fatalf("Was able to read back deleted recipe")
+		}
+
+		return nil
+	})
 }