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//
// A DBQuery which is explained rather than executed normally. Also could be thought of as
// an "explainable cursor". Explains of .find() operations run through this abstraction.
//
var DBExplainQuery = (function() {
//
// Private methods.
//
/**
* Many of the methods of an explain query just pass through to the underlying
* non-explained DBQuery. Use this to generate a function which calls function 'name' on
* 'destObj' and then returns this.
*/
function createDelegationFunc(explainQuery, dbQuery, name) {
return function() {
dbQuery[name].apply(dbQuery, arguments);
return explainQuery;
};
}
function constructor(query, verbosity) {
//
// Private vars.
//
this._query = query;
this._verbosity = Explainable.parseVerbosity(verbosity);
this._mongo = query._mongo;
this._finished = false;
// Used if this query is a count, not a find.
this._isCount = false;
this._applySkipLimit = false;
//
// Public delegation methods. These just pass through to the underlying
// DBQuery.
//
var delegationFuncNames = [
"addOption",
"allowDiskUse",
"batchSize",
"collation",
"comment",
"hint",
"limit",
"max",
"maxTimeMS",
"min",
"readPref",
"showDiskLoc",
"skip",
"sort",
];
// Generate the delegation methods from the list of their names.
var that = this;
delegationFuncNames.forEach(function(name) {
that[name] = createDelegationFunc(that, that._query, name);
});
//
// Core public methods.
//
/**
* Indicates that we are done building the query to explain, and sends the explain
* command or query to the server.
*
* Returns the result of running the explain.
*/
this.finish = function() {
if (this._finished) {
throw Error("query has already been explained");
}
// Mark this query as finished. Shouldn't be used for another explain.
this._finished = true;
// Explain always gets pretty printed.
this._query._prettyShell = true;
// Convert this explain query into an explain command, and send the command to
// the server.
var innerCmd;
if (this._isCount) {
// True means to always apply the skip and limit values.
innerCmd = this._query._convertToCountCmd(this._applySkipLimit);
} else {
innerCmd = this._query._convertToCommand();
}
var explainCmd = {explain: innerCmd};
explainCmd["verbosity"] = this._verbosity;
// If "maxTimeMS" or "$readPreference" are set on 'innerCmd', they need to be
// propagated to the top-level of 'explainCmd' in order to have the intended effect.
if (innerCmd.hasOwnProperty("maxTimeMS")) {
explainCmd.maxTimeMS = innerCmd.maxTimeMS;
}
if (innerCmd.hasOwnProperty("$readPreference")) {
explainCmd["$readPreference"] = innerCmd["$readPreference"];
}
var explainDb = this._query._db;
var explainResult = explainDb.runReadCommand(explainCmd, null, this._query._options);
return Explainable.throwOrReturn(explainResult);
};
this.next = function() {
return this.finish();
};
this.hasNext = function() {
return !this._finished;
};
this.forEach = function(func) {
while (this.hasNext()) {
func(this.next());
}
};
/**
* Returns the explain resulting from running this query as a count operation.
*
* If 'applySkipLimit' is true, then the skip and limit values set on this query values are
* passed to the server; otherwise they are ignored.
*/
this.count = function(applySkipLimit) {
this._isCount = true;
if (applySkipLimit) {
this._applySkipLimit = true;
}
return this.finish();
};
/**
* This gets called automatically by the shell in interactive mode. It should
* print the result of running the explain.
*/
this.shellPrint = function() {
var result = this.finish();
return tojson(result);
};
/**
* Display help text.
*/
this.help = function() {
print("Explain query methods");
print("\t.finish() - sends explain command to the server and returns the result");
print("\t.forEach(func) - apply a function to the explain results");
print("\t.hasNext() - whether this explain query still has a result to retrieve");
print("\t.next() - alias for .finish()");
print("Explain query modifiers");
print("\t.addOption(n)");
print("\t.batchSize(n)");
print("\t.comment(comment)");
print("\t.collation(collationSpec)");
print("\t.count()");
print("\t.hint(hintSpec)");
print("\t.limit(n)");
print("\t.maxTimeMS(n)");
print("\t.max(idxDoc)");
print("\t.min(idxDoc)");
print("\t.readPref(mode, tagSet)");
print("\t.showDiskLoc()");
print("\t.skip(n)");
print("\t.sort(sortSpec)");
return __magicNoPrint;
};
}
return constructor;
})();
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