One more query DSL composition example, introduce monger.query/partial-query

src/monger/query.clj

@@ -34,18 +34,19 @@
 ;;    deleted during the query, it may or may not be returned, even with snapshot mode). Note that short query responses
 ;;    (less than 1MB) are always effectively snapshotted. Currently, snapshot mode may not be used with sorting or explicit hints.
 (defn empty-query
-  [^DBCollection coll]
-  {
-   :collection      coll
-   :query           {}
-   :sort            {}
-   :fields          []
-   :skip            0
-   :limit           0
-   :batch-size      256
-   :hint            nil
-   :snapshot        false
-   })
+  ([]
+     {
+      :query           {}
+      :sort            {}
+      :fields          []
+      :skip            0
+      :limit           0
+      :batch-size      256
+      :hint            nil
+      :snapshot        false
+      })
+  ([^DBCollection coll]
+     (merge (empty-query) { :collection coll })))
 
 (defn- fields-to-db-object
   [^List fields]
@@ -117,3 +118,7 @@
                                   ~coll)]
      (let [query# (-> (empty-query *query-collection*) ~@body)]
        (exec query#))))
+
+(defmacro partial-query
+  [& body]
+  `(-> {} ~@body))

test/monger/test/querying.clj

@@ -216,3 +216,20 @@
     (is (= [doc1 doc5 doc7] result1))
     (is (= [doc2 doc6 doc4] result2))
     (is (= [doc3] result3))))
+
+
+(deftest combined-querying-dsl-example1
+  (let [coll "docs"
+        ma-doc { :_id (ObjectId.) :name "Massachusetts" :iso "MA" :population 6547629  :joined_in 1788 :capital "Boston" }
+        de-doc { :_id (ObjectId.) :name "Delaware"      :iso "DE" :population 897934   :joined_in 1787 :capital "Dover"  }
+        ny-doc { :_id (ObjectId.) :name "New York"      :iso "NY" :population 19378102 :joined_in 1788 :capital "Albany" }
+        ca-doc { :_id (ObjectId.) :name "California"    :iso "CA" :population 37253956 :joined_in 1850 :capital "Sacramento" }
+        tx-doc { :_id (ObjectId.) :name "Texas"         :iso "TX" :population 25145561 :joined_in 1845 :capital "Austin" }
+        top3               (partial-query (limit 3))
+        by-population-desc (partial-query (sort { :population -1 }))
+        _                  (mgcol/insert-batch coll [ma-doc de-doc ny-doc ca-doc tx-doc])
+        result             (with-collection coll
+                             (find {})
+                             (merge top3)
+                             (merge by-population-desc))]
+    (is (= result [ca-doc tx-doc ny-doc]))))