Add support for tsquery_phrase which was added in PostgreSQL 9.6

Author: rwasef1830

src/EntityFramework6.Npgsql/NpgsqlTextFunctions.cs

@@ -370,6 +370,29 @@ public static string TsRewrite(string query, string target, string substitute)
             throw new NotSupportedException();
         }
 
+        /// <summary>
+        /// Returns a tsquery that searches for a match to <paramref name="query1" /> followed by a match
+        /// to <paramref name="query2" />.
+        /// https://www.postgresql.org/docs/current/static/textsearch-features.html#TEXTSEARCH-MANIPULATE-TSQUERY
+        /// </summary>
+        [DbFunction("Npgsql", "tsquery_phrase")]
+        public static string TsQueryPhrase(string query1, string query2)
+        {
+            throw new NotSupportedException();
+        }
+
+        /// <summary>
+        /// Returns a tsquery that searches for a match to <paramref name="query1" /> followed by a match
+        /// to <paramref name="query2" /> at a distance of <paramref name="distance" /> lexemes using 
+        /// the &lt;N&gt; tsquery operator
+        /// https://www.postgresql.org/docs/current/static/textsearch-features.html#TEXTSEARCH-MANIPULATE-TSQUERY
+        /// </summary>
+        [DbFunction("Npgsql", "tsquery_phrase")]
+        public static string TsQueryPhrase(string query1, string query2, int distance)
+        {
+            throw new NotSupportedException();
+        }
+
         /// <summary>
         /// Matches regular expression. Generates the "~" operator.
         /// http://www.postgresql.org/docs/current/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP

test/EntityFramework6.Npgsql.Tests/FullTextSearchTests.cs

@@ -602,5 +602,31 @@ public void TsRewrite()
                     Is.EqualTo(NpgsqlTsQuery.Parse("'b' & ( 'foo' | 'bar' )").ToString()));
             }
         }
+
+        [Test]
+        public void TsQueryPhrase()
+        {
+            using (var context = new BloggingContext(ConnectionString))
+            {
+                context.Database.Log = Console.Out.WriteLine;
+
+                var blog1 = new Blog
+                {
+                    Name = "_"
+                };
+                context.Blogs.Add(blog1);
+                context.SaveChanges();
+
+                var newQuery = context
+                    .Blogs.Select(x => NpgsqlTextFunctions.TsQueryPhrase("b", "c"))
+                    .FirstOrDefault();
+                Assert.That(newQuery, Is.EqualTo("'b' <-> 'c'"));
+
+                newQuery = context
+                    .Blogs.Select(x => NpgsqlTextFunctions.TsQueryPhrase("b", "c", 10))
+                    .FirstOrDefault();
+                Assert.That(newQuery, Is.EqualTo("'b' <10> 'c'"));
+            }
+        }
     }
 }