查询和更新

查询和更新

搭建好项目开发环境后，我们准备创建我们的待办事项列表并进行查询。

创建待办事项

我们先在可测试示例中创建一个 Todo。 我们将以下代码添加到 example_test.go 来完成这项工作：

func Example_Todo() {
    // ...
    task1, err := client.Todo.Create().Save(ctx)
    if err != nil {
        log.Fatalf("failed creating a todo: %v", err)
    }
    fmt.Println(task1)
    // Output:
    // Todo(id=1)
}

执行 go test，它应该是能通过测试的。

添加字段到表结构

正如你看到的，我们的 Todo 只有一个 ID 字段，什么事也做不了。 让我们来改进它，在 todo/ent/schema/todo.go 中给它增加一些字段：

func (Todo) Fields() []ent.Field {
    return []ent.Field{
        field.Text("text").
            NotEmpty(),
        field.Time("created_at").
            Default(time.Now).
            Immutable(),
        field.Enum("status").
            NamedValues(
                "InProgress", "IN_PROGRESS",
                "Completed", "COMPLETED",
            ).
            Default("IN_PROGRESS"),
        field.Int("priority").
            Default(0),
    }
}

添加完这些字段后，我们需要像之前一样执行代码生成：

go generate ./ent

你可能注意到了，除了 text 字段，其他字段在创建时都有一个默认值，唯独它必须由用户提供。 让我们修改 example_test.go 来适配刚刚的变动：

func Example_Todo() {
    // ...
    task1, err := client.Todo.Create().SetText("Add GraphQL Example").Save(ctx)
    if err != nil {
        log.Fatalf("failed creating a todo: %v", err)
    }
    fmt.Printf("%d: %q\n", task1.ID, task1.Text)
    task2, err := client.Todo.Create().SetText("Add Tracing Example").Save(ctx)
    if err != nil {
        log.Fatalf("failed creating a todo: %v", err)
    }
    fmt.Printf("%d: %q\n", task2.ID, task2.Text)
    // Output:
    // 1: "Add GraphQL Example"
    // 2: "Add Tracing Example"
}

很好！ 我们在数据库中成功创建了一张表，包含了 5 列 (id, text, created_at, status, priority)，并且通过插入了两行数据到表中；即我们创建了两个任务到我们的 Todo list 中。

Add Edges To The Schema

Let’s say we want to design our todo list so that an item can depend on another item. Therefore, we’ll add a parent edge to each Todo item, to get the item it depends on, and a back-reference edge named children in order to get all items that depend on it.

Let’s change our schema again in todo/ent/schema/todo.go:

func (Todo) Edges() []ent.Edge {
    return []ent.Edge{
        edge.To("parent", Todo.Type).
            Unique().
            From("children"),
    }
}

After adding these edges, we need to run the code-generation as before:

go generate ./ent

Connect 2 Todos

We continue our edges example, by updating the 2 todo items we just created. We define that item-2 (“Add Tracing Example”) depends on item-1 (“Add GraphQL Example”).

func Example_Todo() {
    // ...
    if err := task2.Update().SetParent(task1).Exec(ctx); err != nil {
        log.Fatalf("failed connecting todo2 to its parent: %v", err)
    }
    // Output:
    // 1: "Add GraphQL Example"
    // 2: "Add Tracing Example"
}

Query Todos

After connecting item-2 to item-1, we’re ready to start querying our todo list.

Query all todo items:

func Example_Todo() {
    // ...

    // Query all todo items.
    items, err := client.Todo.Query().All(ctx)
    if err != nil {
        log.Fatalf("failed querying todos: %v", err)
    }
    for _, t := range items {
        fmt.Printf("%d: %q\n", t.ID, t.Text)
    }
    // Output:
    // 1: "Add GraphQL Example"
    // 2: "Add Tracing Example"
}

Query all todo items that depend on other items:

func Example_Todo() {
    // ...

    // Query all todo items that depend on other items.
    items, err := client.Todo.Query().Where(todo.HasParent()).All(ctx)
    if err != nil {
        log.Fatalf("failed querying todos: %v", err)
    }
    for _, t := range items {
        fmt.Printf("%d: %q\n", t.ID, t.Text)
    }
    // Output:
    // 2: "Add Tracing Example"
}

Query all todo items that don’t depend on other items and have items that depend on them:

func Example_Todo() {
    // ...

    // Query all todo items that don't depend on other items and have items that depend them.
    items, err := client.Todo.Query().
        Where(
            todo.Not(
                todo.HasParent(),
            ),
            todo.HasChildren(),
        ).
        All(ctx)
    if err != nil {
        log.Fatalf("failed querying todos: %v", err)
    }
    for _, t := range items {
        fmt.Printf("%d: %q\n", t.ID, t.Text)
    }
    // Output:
    // 1: "Add GraphQL Example"
}

Query parent through its children:

func Example_Todo() {
    // ...

    // Get a parent item through its children and expect the
    // query to return exactly one item.
    parent, err := client.Todo.Query(). // Query all todos.
        Where(todo.HasParent()).        // Filter only those with parents.
        QueryParent().                  // Continue traversals to the parents.
        Only(ctx)                       // Expect exactly one item.
    if err != nil {
        log.Fatalf("failed querying todos: %v", err)
    }
    fmt.Printf("%d: %q\n", parent.ID, parent.Text)
    // Output:
    // 1: "Add GraphQL Example"
}