Add ByExternallyManagedHashPartitions method

src/CoreTests/Partitioning/partitioning_documents_on_duplicate_fields.cs

@@ -38,7 +38,7 @@ public static void configure_partitioning()
         {
             opts.Connection("some connection string");
 
-            // Set up table partitioning for the User document type
+            // Set up table partitioning for the User document type using RANGE partitioning
             opts.Schema.For<User>()
                 .PartitionOn(x => x.Age, x =>
                 {
@@ -48,24 +48,14 @@ public static void configure_partitioning()
                         .AddRange("thirties", 31, 39);
                 });
 
-            // Or use pg_partman to manage partitioning outside of Marten
-            opts.Schema.For<User>()
-                .PartitionOn(x => x.Age, x =>
-                {
-                    x.ByExternallyManagedRangePartitions();
-
-                    // or instead with list
-
-                    x.ByExternallyManagedListPartitions();
-                });
-
             // Or use PostgreSQL HASH partitioning and split the users over multiple tables
             opts.Schema.For<User>()
                 .PartitionOn(x => x.UserName, x =>
                 {
                     x.ByHash("one", "two", "three");
                 });
 
+            // Or use PostgreSQL LIST partitioning and split the users over multiple tables
             opts.Schema.For<Issue>()
                 .PartitionOn(x => x.Status, x =>
                 {
@@ -76,6 +66,21 @@ public static void configure_partitioning()
                         .AddPartition("new", "New");
                 });
 
+            // Or use pg_partman to manage partitioning outside of Marten
+            opts.Schema.For<User>()
+                .PartitionOn(x => x.Age, x =>
+                {
+                    x.ByExternallyManagedRangePartitions();
+
+                    // or instead with list
+
+                    x.ByExternallyManagedListPartitions();
+
+                    // or instead with hash
+
+                    x.ByExternallyManagedHashPartitions();
+                });
+
         });
 
         #endregion

src/Marten/PartitioningExpression.cs

@@ -15,6 +15,17 @@ public PartitioningExpression(DocumentMapping mapping, string[] columnNames)
         _columnNames = columnNames;
     }
 
+    /// <summary>
+    /// Direct Marten to use PostgreSQL HASH-based partitioning, but to allow the partitions to be managed
+    /// externally from Marten
+    /// </summary>
+    public void  ByExternallyManagedHashPartitions()
+    {
+        _mapping.IgnorePartitions = true;
+        var partitioning = new HashPartitioning { Columns = _columnNames };
+        _mapping.Partitioning = partitioning;
+    }
+
     /// <summary>
     /// Direct Marten to apply equally sized PostgreSQL HASH-based partitioning with a partition for
     /// each named partition suffix