要设置文本属性替换该行code：

  deviceSubscription.setProperty（PROPERTY_SUBSCRIPTION_IDS，this.gson.toJson（订阅））;
 

这一行：

  deviceSubscription.setProperty（PROPERTY_SUBSCRIPTION_IDS，新文本（this.gson.toJson（订阅）））;
 

要获得文本从数据存储属性：

替换该行：

 字符串subscriptionString =（字符串）deviceSubscription.getProperty（PROPERTY_SUBSCRIPTION_IDS）;
 

这一点：

 文本文本=（文本）deviceSubscription.getProperty（PROPERTY_SUBSCRIPTION_IDS）;
    串subscriptionString = text.getValue（）;
 

替换该行：

 字符串ID =（字符串）deviceSubscription.getProperty（PROPERTY_SUBSCRIPTION_IDS）;
 

这一点：

 文本文本=（文本）deviceSubscription.getProperty（PROPERTY_SUBSCRIPTION_IDS）;
      字符串ID = text.getValue（）;
 

替换该行：

 的String [] IDS =新GSON（）。fromJson（（字符串）entity.getProperty（PROPERTY_SUBSCRIPTION_IDS）
            的String []类）。
 

这一点：

 文本文本=（文本）entity.getProperty（PROPERTY_SUBSCRIPTION_IDS）;
        。的String [] IDS =新GSON（）fromJson（text.getValue（）的String []类。）;
 

似乎是有效的解决办法。我还没有发现负面影响我的项目至今。

注意：作为文档说明文本是没有索引，可以在查询过滤器不能使用，排序顺序。因此，这种限制可能会导致另一个问题，如果物业 SubscriptionIDs 要求进行索引。

When I use the subscribeToCloudMessage() function with CloudBackendMessaging.TOPIC_ID_BROADCAST as the topicId as is done in CloudBackendFragment.java everything works fine but when I give this function my own string I get this message:

error:

m.google.api.client.googleapis.json.GoogleJsonResponseException: 400 Bad Request

"code": 400,
"errors": [
  {
    "domain": "global",
    "message": "SubscriptionIDs: String properties must be 500 characters or less.  Instead, use com.google.appengine.api.datastore.Text, which can store strings of any length.",
    "reason": "badRequest"
  }
],
"message": "SubscriptionIDs: String properties must be 500 characters or less.  Instead, use com.google.appengine.api.datastore.Text, which can store strings of any length."

at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:111)
at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:38)
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest$1.interceptResponse(AbstractGoogleClientRequest.java:312)
at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:1042)
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:410)
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:343)
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:460)
at com.google.cloud.backend.core.CloudBackend.list(CloudBackend.java:314)
at com.google.cloud.backend.core.CloudBackendAsync.access$8(CloudBackendAsync.java:1)
at com.google.cloud.backend.core.CloudBackendAsync$9.callBackend(CloudBackendAsync.java:270)
at com.google.cloud.backend.core.CloudBackendAsync$9.callBackend(CloudBackendAsync.java:1)
at com.google.cloud.backend.core.CloudBackendAsync$BackendCaller.run(CloudBackendAsync.java:402)

This error message means that property SubscriptionIDs (you can find it under the _DeviceSubscription Kind in your datastore) value exceeds 500 Unicode characters limit. Read docs for the reference.

From the docs:

For text strings and unencoded binary data (byte strings), the Datastore supports two value types:

The reason for this happening is that MBS trying to write all subscriptions into one property.

So to overcome this issue we need to use Text instead of String type in MBS backend source code for the SubscriptionIDs property. To do so you need to make following changes in DeviceSubscription.java class:

To set Text property replace this line of code:

deviceSubscription.setProperty(PROPERTY_SUBSCRIPTION_IDS, this.gson.toJson(subscriptions));

with this line:

deviceSubscription.setProperty(PROPERTY_SUBSCRIPTION_IDS, new Text(this.gson.toJson(subscriptions)));

To get Text property from the datastore:

Replace this line:

String subscriptionString = (String) deviceSubscription.getProperty(PROPERTY_SUBSCRIPTION_IDS);

with this:

Text text = (Text) deviceSubscription.getProperty(PROPERTY_SUBSCRIPTION_IDS);
    String subscriptionString = text.getValue();

Replace this line:

String ids = (String) deviceSubscription.getProperty(PROPERTY_SUBSCRIPTION_IDS);

with this:

Text text = (Text) deviceSubscription.getProperty(PROPERTY_SUBSCRIPTION_IDS);
      String ids = text.getValue();

Replace this line:

String[] ids = new Gson().fromJson((String) entity.getProperty(PROPERTY_SUBSCRIPTION_IDS),
            String[].class);

with this:

Text text = (Text) entity.getProperty(PROPERTY_SUBSCRIPTION_IDS);
        String[] ids = new Gson().fromJson(text.getValue(), String[].class);

Seems to be valid solution. I have not noticed negative influence on my project so far.

NOTE: As docs stated Text is not indexed and cannot be used in query filters and sort orders. So this limitation could have cause another issues if the property SubscriptionIDs required to be indexed.