Add SqliteConnection.CreateCollation method

src/Microsoft.Data.Sqlite.Core/SqliteConnection.cs

@@ -264,6 +264,27 @@ protected override void Dispose(bool disposing)
         protected override DbCommand CreateDbCommand()
             => CreateCommand();
 
+        /// <summary>
+        /// Create custom collation.
+        /// </summary>
+        /// <param name="name">Name of the collation.</param>
+        /// <param name="comparison">Method that compares two strings.</param>
+        public virtual void CreateCollation(string name, Comparison<string> comparison)
+            => CreateCollation<object>(name, null, (_, s1, s2) => comparison(s1, s2));
+
+        /// <summary>
+        /// Create custom collation.
+        /// </summary>
+        /// <typeparam name="T">The type of the state object.</typeparam>
+        /// <param name="name">Name of the collation.</param>
+        /// <param name="state">State object passed to each invokation of the collation.</param>
+        /// <param name="comparison">Method that compares two strings, using additional state.</param>
+        public virtual void CreateCollation<T>(string name, T state, Func<T, string, string, int> comparison)
+        {
+            var rc = raw.sqlite3_create_collation(_db, name, state, (v, s1, s2) => comparison((T)v, s1, s2));
+            SqliteException.ThrowExceptionForRC(rc, _db);
+        }
+
         /// <summary>
         /// Begins a transaction on the connection.
         /// </summary>

test/Microsoft.Data.Sqlite.Tests/SqliteConnectionTest.cs

@@ -1,7 +1,8 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 using System.Data;
 using System.IO;
 using Microsoft.Data.Sqlite.Properties;
@@ -310,6 +311,40 @@ public void CreateCommand_returns_command()
             }
         }
 
+        [Fact]
+        public void CreateCollation_works()
+        {
+            using (var connection = new SqliteConnection("Data Source=:memory:"))
+            {
+                connection.Open();
+                connection.CreateCollation("MY_NOCASE", (s1, s2) => string.Compare(s1, s2, StringComparison.OrdinalIgnoreCase));
+
+                Assert.Equal(1L, connection.ExecuteScalar<long>("SELECT 'Νικοσ' = 'ΝΙΚΟΣ' COLLATE MY_NOCASE;"));
+            }
+        }
+
+        [Fact]
+        public void CreateCollation_works_with_state()
+        {
+            using (var connection = new SqliteConnection("Data Source=:memory:"))
+            {
+                connection.Open();
+                var list = new List<string>();
+                connection.CreateCollation<List<string>>(
+                    "MY_NOCASE",
+                    list,
+                    (l, s1, s2) =>
+                    {
+                        l.Add("Invoked");
+                        return string.Compare(s1, s2, StringComparison.OrdinalIgnoreCase);
+                    });
+
+                Assert.Equal(1L, connection.ExecuteScalar<long>("SELECT 'Νικοσ' = 'ΝΙΚΟΣ' COLLATE MY_NOCASE;"));
+                Assert.Equal(1, list.Count);
+                Assert.Equal("Invoked", list[0]);
+            }
+        }
+
         [Fact]
         public void BeginTransaction_throws_when_closed()
         {