Handle PG 10 IDENTITY in resultset metadata

Fixes #1789

(cherry picked from commit 44f34bf)

src/Npgsql/Schema/DbColumnSchemaGenerator.cs

@@ -30,9 +30,13 @@ internal DbColumnSchemaGenerator(NpgsqlConnection connection, RowDescriptionMess
 
         #region Columns queries
 
-        static string GenerateColumnsQuery(string columnFieldFilter) =>
+        static string GenerateColumnsQuery(Version pgVersion, string columnFieldFilter) =>
+            pgVersion < new Version(8, 2)
+                ? GenerateOldColumnsQuery(columnFieldFilter)
+                :
 $@"SELECT
      typ.oid AS typoid, nspname, relname, attname, typ.typname, attrelid, attnum, attnotnull,
+     {(pgVersion >= new Version(10, 0) ? "attidentity != ''" : "FALSE")} AS isidentity,
      CASE WHEN typ.typtype = 'd' THEN typ.typtypmod ELSE atttypmod END AS typmod,
      CASE WHEN atthasdef THEN (SELECT pg_get_expr(adbin, cls.oid) FROM pg_attrdef WHERE adrelid = cls.oid AND adnum = attr.attnum) ELSE NULL END AS default,
      CASE WHEN col.is_updatable = 'YES' THEN true ELSE false END AS is_updatable,
@@ -115,9 +119,7 @@ internal ReadOnlyCollection<NpgsqlDbColumn> GetColumnSchema()
 
             if (_fetchAdditionalInfo && columnFieldFilter != "")
             {
-                var query = _connection.PostgreSqlVersion >= new Version(8, 2)
-                    ? GenerateColumnsQuery(columnFieldFilter)
-                    : GenerateOldColumnsQuery(columnFieldFilter);
+                var query = GenerateColumnsQuery(_connection.PostgreSqlVersion, columnFieldFilter);
 
 #if NETSTANDARD1_3
                 using (var connection = _connection.Clone())
@@ -196,7 +198,8 @@ NpgsqlDbColumn LoadColumnDefinition(NpgsqlDataReader reader, TypeHandlerRegistry
             var defaultValueOrdinal = reader.GetOrdinal("default");
             column.DefaultValue = reader.IsDBNull(defaultValueOrdinal) ? null : reader.GetString(defaultValueOrdinal);
 
-            column.IsAutoIncrement = column.DefaultValue != null && column.DefaultValue.StartsWith("nextval(");
+            column.IsAutoIncrement = reader.GetBoolean(reader.GetOrdinal("isidentity")) ||
+                column.DefaultValue != null && column.DefaultValue.StartsWith("nextval(");
 
             ColumnPostConfig(column, reader.GetInt32(reader.GetOrdinal("typmod")));
 

test/Npgsql.Tests/ReaderNewSchemaTests.cs

@@ -21,6 +21,7 @@
 // TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 #endregion
 
+using System;
 using System.Data;
 using System.Linq;
 using Npgsql.PostgresTypes;
@@ -245,9 +246,31 @@ public void IsAutoIncrement()
                 using (var reader = cmd.ExecuteReader(CommandBehavior.SchemaOnly | CommandBehavior.KeyInfo))
                 {
                     var columns = reader.GetColumnSchema();
-                    Assert.That(columns[0].IsAutoIncrement, Is.True);
-                    Assert.That(columns[1].IsAutoIncrement, Is.False);
-                    Assert.That(columns[2].IsAutoIncrement, Is.Null);
+                    Assert.That(columns[0].IsAutoIncrement, Is.True, "Serial not identified as autoincrement");
+                    Assert.That(columns[1].IsAutoIncrement, Is.False, "Regular int column identified as autoincrement");
+                    Assert.That(columns[2].IsAutoIncrement, Is.Null, "Literal int identified as autoincrement");
+                }
+            }
+        }
+
+        [Test]
+        public void IsAutoIncrementIdentity()
+        {
+            using (var conn = OpenConnection())
+            {
+                if (conn.PostgreSqlVersion < new Version(10, 0))
+                    Assert.Ignore("IDENTITY introduced in PostgreSQL 10");
+
+                conn.ExecuteNonQuery("CREATE TEMP TABLE data (inc SERIAL, identity INT GENERATED BY DEFAULT AS IDENTITY, non_inc INT)");
+
+                using (var cmd = new NpgsqlCommand("SELECT inc,identity,non_inc,8 FROM data", conn))
+                using (var reader = cmd.ExecuteReader(CommandBehavior.SchemaOnly | CommandBehavior.KeyInfo))
+                {
+                    var columns = reader.GetColumnSchema();
+                    Assert.That(columns[0].IsAutoIncrement, Is.True, "Serial not identified as autoincrement");
+                    Assert.That(columns[1].IsAutoIncrement, Is.True, "PG 10 IDENTITY not identified as autoincrement");
+                    Assert.That(columns[2].IsAutoIncrement, Is.False, "Regular int column identified as autoincrement");
+                    Assert.That(columns[3].IsAutoIncrement, Is.Null, "Literal int identified as autoincrement");
                 }
             }
         }