关于Apache Ignite中qryexe的跨缓存查询及结果转换问题

Hey there! Let's tackle your two questions about qryfldexe and qryexe step by step:

1. Does qryexe support cross-cache queries with multiple joins? #

From what I know, qryfldexe is built specifically to handle cross-cache multi-join queries and returns value-only arrays as results. However, qryexe doesn't natively support cross-cache multi-joins out of the box. Its core design focuses on returning key-value pair results, making it optimized for single-cache, direct key-based lookups rather than complex cross-cache join operations.

That said, you can work around this limitation in a couple of ways:

• Use qryfldexe to run the cross-cache join first, then map its array results into key-value pairs in your application code.
• Execute separate qryexe queries against different caches, then manually handle the join logic at the application layer (though this might be less efficient than letting qryfldexe handle the join directly).

2. Java tools to convert qryfldexe results to JSON objects #

There's no dedicated library for this task, but you can easily build a solution using popular Java JSON processing libraries like Jackson or Gson. The core idea is to parse the qryfldexe payload, extract the leading field metadata, then map each subsequent value array to a key-value pair object.

Here's a practical example using Jackson:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class QryFldExeConverter {
    public static List<Map<String, Object>> convertToJsonObjects(String qryFldExePayload) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode rootNode = objectMapper.readTree(qryFldExePayload);
        
        List<String> fieldNames = new ArrayList<>();
        List<Map<String, Object>> jsonObjects = new ArrayList<>();

        // Split field metadata and value rows from the payload
        for (JsonNode node : rootNode) {
            if (node.isArray() && !fieldNames.isEmpty() && node.size() == fieldNames.size()) {
                // Map value array to key-value pairs
                Map<String, Object> rowMap = new HashMap<>();
                for (int i = 0; i < fieldNames.size(); i++) {
                    JsonNode valueNode = node.get(i);
                    // Adjust type conversion based on your actual data types
                    if (valueNode.isInt()) {
                        rowMap.put(fieldNames.get(i), valueNode.asInt());
                    } else if (valueNode.isBoolean()) {
                        rowMap.put(fieldNames.get(i), valueNode.asBoolean());
                    } else {
                        rowMap.put(fieldNames.get(i), valueNode.asText());
                    }
                }
                jsonObjects.add(rowMap);
            } else {
                // Collect field names from the payload header
                fieldNames.add(node.asText());
            }
        }
        return jsonObjects;
    }
}

This code takes the raw JSON payload from qryfldexe, separates the field names from the value rows, then converts each row into a Map (which can be easily serialized to a JSON object). You can tweak the type conversion logic to match the actual data types returned by your queries.

内容的提问来源于stack exchange，提问作者Eric