check explain supported in individual op classes

Author: HanaPearlman

src/cmap/wire_protocol/write_command.ts

@@ -67,11 +67,9 @@ export function writeCommand(
 
   // If a command is to be explained, we need to reformat the command after
   // the other command properties are specified.
-  if (options.explain !== undefined) {
-    const explain = Explain.fromOptions(options);
-    if (explain) {
-      writeCommand = decorateWithExplain(writeCommand, explain);
-    }
+  const explain = Explain.fromOptions(options);
+  if (explain) {
+    writeCommand = decorateWithExplain(writeCommand, explain);
   }
 
   const commandOptions = Object.assign(

src/explain.ts

@@ -1,7 +1,4 @@
-import type { Document } from '.';
 import { MongoError } from './error';
-import type { Server } from './sdam/server';
-import { maxWireVersion } from './utils';
 
 /** @public */
 export const ExplainVerbosity = {
@@ -24,13 +21,6 @@ export interface ExplainOptions {
   explain?: ExplainVerbosityLike;
 }
 
-// Minimum server versions which support explain with specific operations
-const SUPPORTS_EXPLAIN_WITH_REMOVE = 3;
-const SUPPORTS_EXPLAIN_WITH_UPDATE = 3;
-const SUPPORTS_EXPLAIN_WITH_DISTINCT = 4;
-const SUPPORTS_EXPLAIN_WITH_FIND_AND_MODIFY = 4;
-const SUPPORTS_EXPLAIN_WITH_MAP_REDUCE = 9;
-
 /** @internal */
 export class Explain {
   verbosity: keyof typeof ExplainVerbosity;
@@ -55,22 +45,4 @@ export class Explain {
 
     throw new MongoError(`explain must be one of ${Object.keys(ExplainVerbosity)} or a boolean`);
   }
-
-  /** Checks that the server supports explain on the given operation or command.*/
-  static explainSupported(server: Server, op: string | Document): boolean {
-    const wireVersion = maxWireVersion(server);
-    if (op === 'remove' || (typeof op === 'object' && op.remove)) {
-      return wireVersion >= SUPPORTS_EXPLAIN_WITH_REMOVE;
-    } else if (op === 'update' || (typeof op === 'object' && op.update)) {
-      return wireVersion >= SUPPORTS_EXPLAIN_WITH_UPDATE;
-    } else if (op === 'distinct' || (typeof op === 'object' && op.distinct)) {
-      return wireVersion >= SUPPORTS_EXPLAIN_WITH_DISTINCT;
-    } else if (op === 'findAndModify' || (typeof op === 'object' && op.findAndModify)) {
-      return wireVersion >= SUPPORTS_EXPLAIN_WITH_FIND_AND_MODIFY;
-    } else if (op === 'mapReduce' || (typeof op === 'object' && op.mapReduce)) {
-      return wireVersion >= SUPPORTS_EXPLAIN_WITH_MAP_REDUCE;
-    }
-
-    return false;
-  }
 }

src/operations/command.ts

@@ -156,11 +156,6 @@ export abstract class CommandOperation<
     }
 
     if (this.hasAspect(Aspect.EXPLAINABLE) && this.explain) {
-      if (!Explain.explainSupported(server, cmd)) {
-        callback(new MongoError(`server ${server.name} does not support explain on this command`));
-        return;
-      }
-
       cmd = decorateWithExplain(cmd, this.explain);
     }
 

src/operations/common_functions.ts

@@ -4,7 +4,8 @@ import {
   applyWriteConcern,
   decorateWithCollation,
   Callback,
-  getTopology
+  getTopology,
+  maxWireVersion
 } from '../utils';
 import type { Document } from '../bson';
 import type { Db } from '../db';
@@ -162,6 +163,12 @@ export function removeDocuments(
     return callback ? callback(err, null) : undefined;
   }
 
+  if (options.explain !== undefined && maxWireVersion(server) < 3) {
+    return callback
+      ? callback(new MongoError(`server ${server.name} does not support explain on remove`))
+      : undefined;
+  }
+
   // Execute the remove
   server.remove(
     coll.s.namespace.toString(),
@@ -254,6 +261,12 @@ export function updateDocuments(
     return callback(err, null);
   }
 
+  if (options.explain !== undefined && maxWireVersion(server) < 3) {
+    return callback
+      ? callback(new MongoError(`server ${server.name} does not support explain on update`))
+      : undefined;
+  }
+
   // Update options
   server.update(
     coll.s.namespace.toString(),

src/operations/distinct.ts

@@ -1,9 +1,10 @@
 import { Aspect, defineAspects } from './operation';
 import { CommandOperation, CommandOperationOptions } from './command';
-import { decorateWithCollation, decorateWithReadConcern, Callback } from '../utils';
+import { decorateWithCollation, decorateWithReadConcern, Callback, maxWireVersion } from '../utils';
 import type { Document } from '../bson';
 import type { Server } from '../sdam/server';
 import type { Collection } from '../collection';
+import { MongoError } from '../error';
 
 /** @public */
 export type DistinctOptions = CommandOperationOptions;
@@ -63,6 +64,11 @@ export class DistinctOperation extends CommandOperation<DistinctOptions, Documen
       return callback(err);
     }
 
+    if (this.explain && maxWireVersion(server) < 4) {
+      callback(new MongoError(`server ${server.name} does not support explain on distinct`));
+      return;
+    }
+
     super.executeCommand(server, cmd, (err, result) => {
       if (err) {
         callback(err);

src/operations/find_and_modify.ts

@@ -143,6 +143,11 @@ export class FindAndModifyOperation extends CommandOperation<FindAndModifyOption
       cmd.hint = options.hint;
     }
 
+    if (this.explain && maxWireVersion(server) < 4) {
+      callback(new MongoError(`server ${server.name} does not support explain on findAndModify`));
+      return;
+    }
+
     // Execute the command
     super.executeCommand(server, cmd, (err, result) => {
       if (err) return callback(err);

src/operations/map_reduce.ts

@@ -5,7 +5,8 @@ import {
   decorateWithCollation,
   decorateWithReadConcern,
   isObject,
-  Callback
+  Callback,
+  maxWireVersion
 } from '../utils';
 import { ReadPreference, ReadPreferenceMode } from '../read_preference';
 import { CommandOperation, CommandOperationOptions } from './command';
@@ -158,6 +159,11 @@ export class MapReduceOperation extends CommandOperation<MapReduceOptions, Docum
       return callback(err);
     }
 
+    if (this.explain && maxWireVersion(server) < 9) {
+      callback(new MongoError(`server ${server.name} does not support explain on mapReduce`));
+      return;
+    }
+
     // Execute command
     super.executeCommand(server, mapCommandHash, (err, result) => {
       if (err) return callback(err);

src/sdam/server.ts

@@ -458,11 +458,6 @@ function executeWriteOperation(
     }
   }
 
-  if (options.explain !== undefined && !Explain.explainSupported(server, op)) {
-    callback(new MongoError(`server ${server.name} does not support explain on ${op}`));
-    return;
-  }
-
   server.s.pool.withConnection((err, conn, cb) => {
     if (err || !conn) {
       markServerUnknown(server, err);

src/utils.ts

@@ -447,7 +447,7 @@ export function decorateWithReadConcern(
  * Applies an explain to a given command.
  * @internal
  *
- * @param command - the command on which to apply the read concern
+ * @param command - the command on which to apply the explain
  * @param options - the options containing the explain verbosity
  */
 export function decorateWithExplain(command: Document, explain: Explain): Document {