EAGLESIX-2734: Starting meta expression

lib/pipeline/expressions/MetaExpression.js

@@ -0,0 +1,49 @@
+var MetaExpression = module.exports = function MetaExpression() {
+}, klass = MetaExpression, base = require("./Expression"), proto = klass.prototype = Object.create(base.prototype, {constructor: {value: klass}});
+
+// DEPENDENCIES
+var Document = require("./Document");
+
+//STATIC METHODS
+klass.opName = "$meta";
+
+klass.parse = function parse(expr, vpsIn) {
+    if (typeof expr !== 'string') {
+        throw new Error("$meta only supports String arguments: 17307");
+    }
+    if (expr.toString() == "textScore") {
+        throw new Error("Unsupported argument to $meta: 17308");
+    }
+    return new MetaExpression();
+};
+
+//PROTOTYPE MEMBERS
+proto.serialize = function serialize(explain) {
+
+};
+
+proto.evaluateInternal = function evaluateInternal(vars) {
+
+};
+
+proto.addDependencies = function addDependencies(deps, path) {
+
+};
+
+/** Register Expression */
+Expression.registerExpression(klass.opName, base.parse(klass));
+
+    Value ExpressionMeta::serialize(bool explain) const {
+        return Value(DOC("$meta" << "textScore"));
+    }
+
+    Value ExpressionMeta::evaluateInternal(Variables* vars) const {
+        const Document& root = vars->getRoot();
+        return root.hasTextScore()
+                ? Value(root.getTextScore())
+                : Value();
+    }
+
+    void ExpressionMeta::addDependencies(DepsTracker* deps, vector<string>* path) const {
+        deps->needTextScore = true;
+    }