Trying to add time stamps to an array in cloud firestore

[CalColistra]

Hello, have been trying to add time stamps of the current time to an array. I'm using firebases REQUEST_TIME to get the current server value as shown in the examples. I can't seem to get it working. I used one of the examples and I got it to transform a single data field, updating the time stamp with the current time but I want to figure out how to have it add a new time stamp to an array field instead.

I believe my error is on the line where I set the transformation type because in the example it uses:
field_transforms.transform_type = fb_esp_firestore_transform_type_set_to_server_value instead of:
field_transforms.transform_type = fb_esp_firestore_transform_type_append_missing_elements;
Currently, when I call this function, it shows that my payload is empty and does not add or change anything in my database.

Is it possible to have my esp32 to add new timestamps to an array field? I apologize if I'm missing something obvious here.

I very much appreciate any help with this.

Here is the code I have so far:

        // The dyamic array of write object fb_esp_firestore_document_write_t.
        std::vector<struct fb_esp_firestore_document_write_t> writes;

        // A write object that will be written to the document.
        struct fb_esp_firestore_document_write_t transform_write;

        // Set the write object write operation type.
        // fb_esp_firestore_document_write_type_update,
        // fb_esp_firestore_document_write_type_delete,
        // fb_esp_firestore_document_write_type_transform
        
        transform_write.type = fb_esp_firestore_document_write_type_transform;

        // Set the document path of document to write (transform)
        transform_write.document_transform.transform_document_path = "test_collection/test_document";

        // Set a transformation of a field of the document.
        struct fb_esp_firestore_document_write_field_transforms_t field_transforms;

        // Set field path to write.
        field_transforms.fieldPath = "server_time";

        // Set the transformation type.
        //field_transforms.transform_type = fb_esp_firestore_transform_type_set_to_server_value;
        field_transforms.transform_type = fb_esp_firestore_transform_type_append_missing_elements;
        
        // Set the transformation content, server value for this case.
        // See https://firebase.google.com/docs/firestore/reference/rest/v1/Write#servervalue
        field_transforms.transform_content = "REQUEST_TIME"; // set timestamp to "test_collection/test_document/server_time"

        // Add a field transformation object to a write object.
        transform_write.document_transform.field_transforms.push_back(field_transforms);

        // Add a write object to a write array.
        writes.push_back(transform_write);

        if (Firebase.Firestore.commitDocument(&fbdo, FIREBASE_PROJECT_ID, "" /* databaseId can be (default) or empty */, writes /* dynamic array of fb_esp_firestore_document_write_t */, "" /* transaction */))
            Serial.printf("ok\n%s\n\n", fbdo.payload().c_str());
        else
            Serial.println(fbdo.errorReason());

[mobizt]

Due to array value has limitations

• we don't know the fields path in the array that contains values.
• we can't get the value at the specific array index, just only can get whole document or whole array inside some filed using query.

Then it's not possible to add the server timestamp to the new appended array or existing array at specific index

The option field_transforms.fieldPath can't be applied to the array.

The only possible way is to create your device (client) timestamp string and add to the data to append.

Instead of using array, using the map value with server timestamp that can be append to some field as in this example is recommend.
And it is suitable for the low memory device to query only the specific field instead of array that we need to get whole array which the device memory may not enough to parse the large array.