feat: Optionally align limit() and tail() before pivot() function

CHANGELOG.md

@@ -1,5 +1,8 @@
 ## 4.2.0 [unreleased]
 
+### Features
+1. [#319](https://github.com/influxdata/influxdb-client-csharp/pull/319): Optionally align `limit()` and `tail()` before `pivot()` function [LINQ]
+
 ### Breaking Changes
 1. [#316](https://github.com/influxdata/influxdb-client-csharp/pull/316): Rename `InvocableScripts` to `InvokableScripts`
 

Client.Linq.Test/InfluxDBQueryVisitorTest.cs

@@ -1108,6 +1108,32 @@ public void FilterByTimeAndTagWithAnds()
             Assert.AreEqual(expected, visitor.BuildFluxQuery());
         }
 
+        [Test]
+        public void AlignLimitFunctionBeforePivot()
+        {
+            var query = from s in InfluxDBQueryable<Sensor>.Queryable("my-bucket", "my-org", _queryApi,
+                    new QueryableOptimizerSettings { AlignLimitFunctionAfterPivot = false })
+                select s;
+
+            var visitor = BuildQueryVisitor(query, MakeExpression(query, q => q.TakeLast(10)));
+            var expected = "start_shifted = int(v: time(v: p2))\n\n" +
+                           "from(bucket: p1) " +
+                           "|> range(start: time(v: start_shifted)) " +
+                           "|> tail(n: p3) " +
+                           "|> pivot(rowKey:[\"_time\"], columnKey: [\"_field\"], valueColumn: \"_value\") " +
+                           "|> drop(columns: [\"_start\", \"_stop\", \"_measurement\"])";
+            Assert.AreEqual(expected, visitor.BuildFluxQuery());
+
+            visitor = BuildQueryVisitor(query, MakeExpression(query, q => q.Take(10)));
+            expected = "start_shifted = int(v: time(v: p2))\n\n" +
+                       "from(bucket: p1) " +
+                       "|> range(start: time(v: start_shifted)) " +
+                       "|> limit(n: p3) " +
+                       "|> pivot(rowKey:[\"_time\"], columnKey: [\"_field\"], valueColumn: \"_value\") " +
+                       "|> drop(columns: [\"_start\", \"_stop\", \"_measurement\"])";
+            Assert.AreEqual(expected, visitor.BuildFluxQuery());
+        }
+
         private InfluxDBQueryVisitor BuildQueryVisitor(IQueryable queryable, Expression expression = null)
         {
             var queryExecutor = (InfluxDBQueryExecutor)((DefaultQueryProvider)queryable.Provider).Executor;

Client.Linq/InfluxDBQueryable.cs

@@ -21,6 +21,7 @@ public QueryableOptimizerSettings()
         {
             QueryMultipleTimeSeries = false;
             AlignFieldsWithPivot = true;
+            AlignLimitFunctionAfterPivot = true;
             DropMeasurementColumn = true;
             DropStartColumn = true;
             DropStopColumn = true;
@@ -42,6 +43,12 @@ public QueryableOptimizerSettings()
         /// </summary>
         public bool AlignFieldsWithPivot { get; set; }
 
+        /// <summary>
+        /// Gets or set whether the drive should align <a>limit()</a> and <a>tail()</a> functions
+        /// after <a href="https://docs.influxdata.com/flux/v0.x/stdlib/universe/pivot/">pivot()</a> function.
+        /// </summary>
+        public bool AlignLimitFunctionAfterPivot { get; set; }
+
         /// <summary>
         /// Gets or sets whether the _measurement column will be dropped from query results.
         /// Setting this variable to true will change how the produced Flux Query looks like:

Client.Linq/Internal/QueryAggregator.cs

@@ -166,12 +166,19 @@ internal string BuildFluxQuery(QueryableOptimizerSettings settings)
                 BuildOperator("from", "bucket", _bucketAssignment),
                 BuildRange(transforms),
                 BuildFilter(_filterByTags),
-                BuildAggregateWindow(_aggregateWindow),
-                settings.AlignFieldsWithPivot
-                    ? "pivot(rowKey:[\"_time\"], columnKey: [\"_field\"], valueColumn: \"_value\")"
-                    : ""
+                BuildAggregateWindow(_aggregateWindow)
             };
 
+            if (!settings.AlignLimitFunctionAfterPivot)
+            {
+                AddLimitFunctions(parts);
+            }
+
+            if (settings.AlignFieldsWithPivot)
+            {
+                parts.Add("pivot(rowKey:[\"_time\"], columnKey: [\"_field\"], valueColumn: \"_value\")");
+            }
+
             var drop = BuildDrop(settings);
             if (!string.IsNullOrEmpty(drop))
             {
@@ -195,14 +202,10 @@ internal string BuildFluxQuery(QueryableOptimizerSettings settings)
                     descendingVariable));
             }
 
-            // https://docs.influxdata.com/flux/v0.x/stdlib/universe/limit/
-            foreach (var limitNOffsetAssignment in _limitTailNOffsetAssignments)
-                if (limitNOffsetAssignment.N != null)
-                {
-                    parts.Add(BuildOperator(limitNOffsetAssignment.FluxFunction,
-                        "n", limitNOffsetAssignment.N,
-                        "offset", limitNOffsetAssignment.Offset));
-                }
+            if (settings.AlignLimitFunctionAfterPivot)
+            {
+                AddLimitFunctions(parts);
+            }
 
             if (_resultFunction != ResultFunction.None)
             {
@@ -223,6 +226,19 @@ internal string BuildFluxQuery(QueryableOptimizerSettings settings)
             return query.ToString();
         }
 
+        private void AddLimitFunctions(List<string> parts)
+        {
+            // https://docs.influxdata.com/flux/latest/stdlib/universe/limit/
+            // https://docs.influxdata.com/flux/latest/stdlib/universe/tail/
+            foreach (var limitNOffsetAssignment in _limitTailNOffsetAssignments)
+                if (limitNOffsetAssignment.N != null)
+                {
+                    parts.Add(BuildOperator(limitNOffsetAssignment.FluxFunction,
+                        "n", limitNOffsetAssignment.N,
+                        "offset", limitNOffsetAssignment.Offset));
+                }
+        }
+
         private string BuildAggregateWindow((string Every, string Period, string Fn)? aggregateWindow)
         {
             if (aggregateWindow == null)

Client.Linq/README.md

@@ -851,6 +851,18 @@ from(bucket: "my-bucket")
     |> limit(n: 10)
 ```
 
+**_Note:_** the `limit()` function can be align before `pivot()` function by:
+
+```c#
+var optimizerSettings =
+    new QueryableOptimizerSettings
+    {
+        AlignLimitFunctionAfterPivot = false
+    };
+```
+
+**_Performance:_** The `pivot()` is a [“heavy” function](https://docs.influxdata.com/influxdb/cloud/query-data/optimize-queries/#use-heavy-functions-sparingly). Using `limit()` before `pivot()` is much faster but works only if you have consistent data series. See [#318](https://github.com/influxdata/influxdb-client-csharp/issues/318) for more details.
+
 ### TakeLast
 
 ```c#
@@ -869,6 +881,17 @@ from(bucket: "my-bucket")
     |> tail(n: 10)
 ```
 
+**_Note:_** the `tail()` function can be align before `pivot()` function by:
+
+```c#
+var optimizerSettings =
+    new QueryableOptimizerSettings
+    {
+        AlignLimitFunctionAfterPivot = false
+    };
+```
+**_Performance:_** The `pivot()` is a [“heavy” function](https://docs.influxdata.com/influxdb/cloud/query-data/optimize-queries/#use-heavy-functions-sparingly). Using `tail()` before `pivot()` is much faster but works only if you have consistent data series. See [#318](https://github.com/influxdata/influxdb-client-csharp/issues/318) for more details.
+
 ### Skip
 
 ```c#

Client.Test/AbstractItClientTest.cs

@@ -3,10 +3,8 @@
 using System.Linq;
 using System.Threading.Tasks;
 using InfluxDB.Client.Api.Domain;
-using InfluxDB.Client.Core;
 using InfluxDB.Client.Core.Test;
 using NUnit.Framework;
-using Task = System.Threading.Tasks.Task;
 
 namespace InfluxDB.Client.Test
 {