資料驗證

您可以使用 Firebase Security Rules，根據資料庫或儲存體值區中的現有資料，有條件地寫入新資料。您也可以撰寫規則，根據要寫入的新資料限制寫入作業，以便強制執行資料驗證。請繼續閱讀，進一步瞭解如何使用現有資料建立安全性條件。

請在各個部分中選取產品，進一步瞭解資料驗證規則。

新資料的限制

Cloud Firestore

如果您想確保系統不會建立包含特定欄位的文件，可以將該欄位納入 allow 條件。舉例來說，如要拒絕建立任何包含 ranking 欄位的文件，您可以在 create 條件中禁止該欄位。

  service cloud.firestore {
    match /databases/{database}/documents {
      // Disallow
      match /cities/{city} {
        allow create: if !("ranking" in request.resource.data)
      }
    }
  }

Realtime Database

如要確保不將含有特定值的資料新增至資料庫，請在規則中加入該值，並禁止寫入。舉例來說，如果您想拒絕任何含有 ranking 值的寫入作業，就應禁止任何含有 ranking 值的文件寫入作業。

  {
    "rules": {
      // Write is allowed for all paths
      ".write": true,
      // Allows writes only if new data doesn't include a `ranking` child value
      ".validate": "!newData.hasChild('ranking')
    }
  }

Cloud Storage

如要確保不會建立包含特定中繼資料的檔案，您可以在 allow 條件中加入中繼資料。舉例來說，如果您想拒絕建立任何含有 ranking 中繼資料的檔案，請在 create 條件中禁止這項操作。

  service firebase.storage {
    match /b/{bucket}/o {
      match /files/{allFiles=**} {
      // Disallow
        allow create: if !("ranking" in request.resource.metadata)
      }
    }
  }

使用 Firebase Security Rules 中的現有資料

Cloud Firestore

許多應用程式會將存取權控管資訊儲存為資料庫中文件的欄位。Cloud Firestore Security Rules 可根據文件資料動態允許或拒絕存取權：

  service cloud.firestore {
    match /databases/{database}/documents {
      // Allow the user to read data if the document has the 'visibility'
      // field set to 'public'
      match /cities/{city} {
        allow read: if resource.data.visibility == 'public';
      }
    }
  }

resource 變數代表要求的文件，而 resource.data 則是文件中儲存的所有欄位和值的對應項目。如要進一步瞭解 resource 變數，請參閱參考說明文件。

寫入資料時，您可能會將傳入的資料與現有資料進行比較。這可讓您執行各種操作，例如確保欄位未變更、欄位只增加 1 個，或是新值至少在未來一週後。在這種情況下，如果規則集允許待寫入的內容，request.resource 變數就會包含文件的未來狀態。對於只修改文件欄位子集的 update 作業，request.resource 變數會在作業後包含待處理的文件狀態。您可以檢查 request.resource 中的欄位值，以免發生不必要或不一致的資料更新：

   service cloud.firestore {
     match /databases/{database}/documents {
      // Make sure all cities have a positive population and
      // the name is not changed
      match /cities/{city} {
        allow update: if request.resource.data.population > 0
                      && request.resource.data.name == resource.data.name;
      }
    }
  }

Realtime Database

在 Realtime Database 中，請使用 .validate 規則強制執行資料結構，並驗證資料的格式和內容。確認 .write 規則已授予存取權後，Rules 就會執行 .validate 規則。

.validate 規則不會層疊。如果任何驗證規則在規則中的任何路徑或子路徑上失敗，整個寫入作業都會遭到拒絕。此外，驗證定義只會檢查非空值，並隨後忽略任何刪除資料的要求。

請考慮下列 .validate 規則：

  {
    "rules": {
      // write is allowed for all paths
      ".write": true,
      "widget": {
        // a valid widget must have attributes "color" and "size"
        // allows deleting widgets (since .validate is not applied to delete rules)
        ".validate": "newData.hasChildren(['color', 'size'])",
        "size": {
          // the value of "size" must be a number between 0 and 99
          ".validate": "newData.isNumber() &&
                        newData.val() >= 0 &&
                        newData.val() <= 99"
        },
        "color": {
          // the value of "color" must exist as a key in our mythical
          // /valid_colors/ index
          ".validate": "root.child('valid_colors/' + newData.val()).exists()"
        }
      }
    }
  }

使用上述規則向資料庫提出寫入要求，會產生以下結果：

JavaScript
var ref = db.ref("/widget");

// PERMISSION_DENIED: does not have children color and size
ref.set('foo');

// PERMISSION DENIED: does not have child color
ref.set({size: 22});

// PERMISSION_DENIED: size is not a number
ref.set({ size: 'foo', color: 'red' });

// SUCCESS (assuming 'blue' appears in our colors list)
ref.set({ size: 21, color: 'blue'});

// If the record already exists and has a color, this will
// succeed, otherwise it will fail since newData.hasChildren(['color', 'size'])
// will fail to validate
ref.child('size').set(99);
Objective-C
注意：這項 Firebase 產品不適用於 App Clip 目標。
FIRDatabaseReference *ref = [[[FIRDatabase database] reference] child: @"widget"];

// PERMISSION_DENIED: does not have children color and size
[ref setValue: @"foo"];

// PERMISSION DENIED: does not have child color
[ref setValue: @{ @"size": @"foo" }];

// PERMISSION_DENIED: size is not a number
[ref setValue: @{ @"size": @"foo", @"color": @"red" }];

// SUCCESS (assuming 'blue' appears in our colors list)
[ref setValue: @{ @"size": @21, @"color": @"blue" }];

// If the record already exists and has a color, this will
// succeed, otherwise it will fail since newData.hasChildren(['color', 'size'])
// will fail to validate
[[ref child:@"size"] setValue: @99];
Swift
注意：這項 Firebase 產品不適用於 App Clip 目標。
var ref = FIRDatabase.database().reference().child("widget")

// PERMISSION_DENIED: does not have children color and size
ref.setValue("foo")

// PERMISSION DENIED: does not have child color
ref.setValue(["size": "foo"])

// PERMISSION_DENIED: size is not a number
ref.setValue(["size": "foo", "color": "red"])

// SUCCESS (assuming 'blue' appears in our colors list)
ref.setValue(["size": 21, "color": "blue"])

// If the record already exists and has a color, this will
// succeed, otherwise it will fail since newData.hasChildren(['color', 'size'])
// will fail to validate
ref.child("size").setValue(99);
Java
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference ref = database.getReference("widget");

// PERMISSION_DENIED: does not have children color and size
ref.setValue("foo");

// PERMISSION DENIED: does not have child color
ref.child("size").setValue(22);

// PERMISSION_DENIED: size is not a number
Map<String,Object> map = new HashMap<String, Object>();
map.put("size","foo");
map.put("color","red");
ref.setValue(map);

// SUCCESS (assuming 'blue' appears in our colors list)
map = new HashMap<String, Object>();
map.put("size", 21);
map.put("color","blue");
ref.setValue(map);

// If the record already exists and has a color, this will
// succeed, otherwise it will fail since newData.hasChildren(['color', 'size'])
// will fail to validate
ref.child("size").setValue(99);
REST
# PERMISSION_DENIED: does not have children color and size
curl -X PUT -d 'foo' \
https://docs-examples.firebaseio.com/rest/securing-data/example.json

# PERMISSION DENIED: does not have child color
curl -X PUT -d '{"size": 22}' \
https://docs-examples.firebaseio.com/rest/securing-data/example.json

# PERMISSION_DENIED: size is not a number
curl -X PUT -d '{"size": "foo", "color": "red"}' \
https://docs-examples.firebaseio.com/rest/securing-data/example.json

# SUCCESS (assuming 'blue' appears in our colors list)
curl -X PUT -d '{"size": 21, "color": "blue"}' \
https://docs-examples.firebaseio.com/rest/securing-data/example.json

# If the record already exists and has a color, this will
# succeed, otherwise it will fail since newData.hasChildren(['color', 'size'])
# will fail to validate
curl -X PUT -d '99' \
https://docs-examples.firebaseio.com/rest/securing-data/example/size.json

Cloud Storage

評估規則時，您可能也會想評估要上傳、下載、修改或刪除檔案的中繼資料。這可讓您建立複雜且強大的規則，例如只允許上傳特定內容類型的檔案，或只刪除超過特定大小的檔案。

resource 物件包含鍵/值組合，其中檔案中繼資料會顯示在 Cloud Storage 物件中。您可以在 read 或 write 要求上檢查這些屬性，確保資料完整性。resource 物件會檢查 Cloud Storage 值區中現有檔案的中繼資料。

  service firebase.storage {
    match /b/{bucket}/o {
      match /images {
        match /{allImages=**} {
          // Allow reads if a custom 'visibility' field is set to 'public'
          allow read: if resource.metadata.visibility == 'public';
        }
      }
    }
  }

您也可以在 write 要求 (例如上傳、中繼資料更新及刪除) 中使用 request.resource 物件。如果允許 write，request.resource 物件會從將要寫入的檔案取得中繼資料。

您可以使用這兩個值來避免不必要或不一致的更新，或是強制應用程式限制，例如檔案類型或大小。

  service firebase.storage {
    match /b/{bucket}/o {
      match /images {
        // Cascade read to any image type at any path
        match /{allImages=**} {
          allow read;
        }

        // Allow write files to the path "images/*", subject to the constraints:
        // 1) File is less than 5MB
        // 2) Content type is an image
        // 3) Uploaded content type matches existing content type
        // 4) File name (stored in imageId wildcard variable) is less than 32 characters
        match /{imageId} {
          allow write: if request.resource.size < 5 * 1024 * 1024
                       && request.resource.contentType.matches('image/.*')
                       && request.resource.contentType == resource.contentType
                       && imageId.size() < 32
        }
      }
    }
  }

如需 resource 物件中的完整屬性清單，請參閱參考說明文件。