社区连接器开发报错：返回列数与Data Studio请求不符

I've run into this exact error multiple times when building dynamic schema connectors for Data Studio, so let's break down what's going on and how to fix it.

Core Cause #

This error happens when the number (and often the identity) of columns your connector returns in getData() doesn't match exactly what was defined in the schema returned by getSchema(). Since your schema is dynamically generated via a REST service, the mismatch is almost certainly coming from inconsistency between the two steps.

Step-by-Step Troubleshooting & Fixes #

1. Validate Schema-Data Field Consistency

   • First, confirm that the fields returned by your REST service during the configuration phase (when getSchema() is called) are exactly the same as what's returned when getData() fetches data. Pay close attention to:
     • Case sensitivity: Data Studio treats field names as case-sensitive. If your schema has userName but your data returns Username, that's a mismatch.
     • Missing/extra fields: If the user selects 5 fields in configuration but your getData() call returns 6 (or 4), you'll get this error.

2. Ensure getData() Respects Requested Fields

   • Data Studio sends the exact fields it needs in request.fields when building the report. Your connector must only return those specific fields from your REST service, not all available fields.
   • Example fix: Modify your getData() function to filter the REST response to only include the fields listed in request.fields:

     function getData(request) {
       // Fetch raw data from your REST service
       const rawData = fetchYourRestData(request.configParams);
       // Filter to only requested fields
       const filteredData = rawData.map(row => {
         const filteredRow = {};
         request.fields.forEach(field => {
           filteredRow[field.name] = row[field.name];
         });
         return filteredRow;
       });
       // Return formatted data to Data Studio
       return {
         schema: request.fields,
         rows: filteredData.map(row => ({ values: Object.values(row) }))
       };
     }
     

3. Check for Schema Caching Issues

   • Google Apps Script may cache the schema returned by getSchema() during configuration. If you've updated your REST service's schema since the last configuration, the cached old schema might be conflicting with new data.
   • Fix: Re-authorize your connector in Data Studio (go to Data Sources > Edit > Reconnect) to force a fresh schema fetch.

4. Verify Field Type Matching

   • While the error mentions column count, mismatched field types can sometimes trigger this error indirectly. Ensure that the type defined in your schema (e.g., STRING, NUMBER, DATE) exactly matches the data type returned by your REST service. For example, don't define a field as NUMBER if your API returns it as a string.

Debugging Tips #

• Add logging to your connector to compare requested vs returned fields:

  function getData(request) {
    console.log("Requested fields: " + JSON.stringify(request.fields.map(f => f.name)));
    const rawData = fetchYourRestData(request.configParams);
    console.log("Raw data fields: " + Object.keys(rawData[0]).join(", "));
    // ... rest of your code
  }
  

  Check the Apps Script logs (View > Logs) to see if there's a mismatch between the two lists.

• Test your REST service directly: Call it with the same parameters used in configuration and in getData() to confirm the field sets are identical.

内容的提问来源于stack exchange，提问作者Diego Convers Laverde