Add "append block children" endpoint support

README.md

@@ -22,7 +22,7 @@ Go client for the [Notion API](https://developers.notion.com/reference).
 ### Blocks
 
 - [x] [Retrieve block children](client.go)
-- [ ] Append block children
+- [x] [Append block children](client.go)
 
 ### Users
 

block.go

@@ -10,7 +10,7 @@ type Block struct {
 	Type           BlockType  `json:"type"`
 	CreatedTime    *time.Time `json:"created_time,omitempty"`
 	LastEditedTime *time.Time `json:"last_edited_time,omitempty"`
-	HasChildren    bool       `json:"has_children"`
+	HasChildren    bool       `json:"has_children,omitempty"`
 
 	Paragraph        *RichTextBlock `json:"paragraph,omitempty"`
 	Heading1         *Heading       `json:"heading_1,omitempty"`

client.go

@@ -261,3 +261,41 @@ func (c *Client) FindBlockChildrenByID(ctx context.Context, blockID string, quer
 
 	return result, nil
 }
+
+// AppendBlockChildren appends child content (blocks) to an existing block.
+// See: https://developers.notion.com/reference/patch-block-children
+func (c *Client) AppendBlockChildren(ctx context.Context, blockID string, children []Block) (block Block, err error) {
+	type PostBody struct {
+		Children []Block `json:"children"`
+	}
+
+	dto := PostBody{children}
+	body := &bytes.Buffer{}
+
+	err = json.NewEncoder(body).Encode(dto)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: failed to encode body params to JSON: %w", err)
+	}
+
+	req, err := c.newRequest(ctx, http.MethodPatch, fmt.Sprintf("/blocks/%v/children", blockID), body)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: invalid request: %w", err)
+	}
+
+	res, err := c.httpClient.Do(req)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: failed to make HTTP request: %w", err)
+	}
+	defer res.Body.Close()
+
+	if res.StatusCode != http.StatusOK {
+		return Block{}, fmt.Errorf("notion: failed to append block children: %w", parseErrorResponse(res))
+	}
+
+	err = json.NewDecoder(res.Body).Decode(&block)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: failed to parse HTTP response: %w", err)
+	}
+
+	return block, nil
+}