FrankChen021 commented on code in PR #13071:
URL: https://github.com/apache/druid/pull/13071#discussion_r990609380
##########
processing/src/main/java/org/apache/druid/query/QueryContext.java:
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@@ -29,227 +33,545 @@
import java.util.TreeMap;
/**
- * Holder for query context parameters. There are 3 ways to set context params
today.
- *
- * - Default parameters. These are set mostly via {@link
DefaultQueryConfig#context}.
- * Auto-generated queryId or sqlQueryId are also set as default parameters.
These default parameters can
- * be overridden by user or system parameters.
- * - User parameters. These are the params set by the user. User params
override default parameters but
- * are overridden by system parameters.
- * - System parameters. These are the params set by the Druid query engine for
internal use only.
- *
- * You can use {@code getX} methods or {@link #getMergedParams()} to compute
the context params
- * merging 3 types of params above.
- *
- * Currently, this class is mainly used for query context parameter
authorization,
- * such as HTTP query endpoints or JDBC endpoint. Its usage can be expanded in
the future if we
- * want to track user parameters and separate them from others during query
processing.
+ * Immutable holder for query context parameters with typed access methods.
+ * Code builds up a map of context values from serialization or during
+ * planning. Once that map is handed to the {@code QueryContext}, that map
+ * is effectively immutable.
+ * <p>
+ * The implementation uses a {@link TreeMap} so that the serialized form of a
query
+ * lists context values in a deterministic order. Jackson will call
+ * {@code getContext()} on the query, which will call {@link #asMap()} here,
+ * which returns the sorted {@code TreeMap}.
+ * <p>
+ * The {@code TreeMap} is a mutable class. We'd prefer an immutable class, but
+ * we can choose either ordering or immutability. Since the semantics of the
context
+ * is that it is immutable once it is placed in a query. Code should NEVER get
the
+ * context map from a query and modify it, even if the actual implementation
+ * allows it.
*/
public class QueryContext
{
- private final Map<String, Object> defaultParams;
- private final Map<String, Object> userParams;
- private final Map<String, Object> systemParams;
+ private static final QueryContext EMPTY = new QueryContext(null);
+
+ private final Map<String, Object> context;
+
+ public QueryContext(Map<String, Object> context)
+ {
+ // There is no semantic difference between an empty and a null context.
+ // Ensure that a context always exists to avoid the need to check for
+ // a null context. Jackson serialization will omit empty contexts.
+ this.context = context == null ? Collections.emptyMap() : new
TreeMap<>(context);
Review Comment:
```suggestion
this.context = context == null ? Collections.emptyMap() :
Collections.unmodifiableMap(new TreeMap<>(context));
```
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