Fix prepare(query:) when no data returned (#123)

* Updated prepared query handling to work when no results are returned

* Added test for issue 122

Author: Jerry-Carter

Sources/PostgresNIO/Connection/PostgresDatabase+PreparedQuery.swift

@@ -5,7 +5,7 @@ extension PostgresDatabase {
         let name = "nio-postgres-\(UUID().uuidString)"
         let prepare = PrepareQueryRequest(query, as: name)
         return self.send(prepare, logger: self.logger).map { () -> (PreparedQuery) in
-            let prepared = PreparedQuery(database: self, name: name, rowDescription: prepare.rowLookupTable!)
+            let prepared = PreparedQuery(database: self, name: name, rowDescription: prepare.rowLookupTable)
             return prepared
         }
     }
@@ -25,9 +25,9 @@ extension PostgresDatabase {
 public struct PreparedQuery {
     let database: PostgresDatabase
     let name: String
-    let rowLookupTable: PostgresRow.LookupTable
+    let rowLookupTable: PostgresRow.LookupTable?
 
-    init(database: PostgresDatabase, name: String, rowDescription: PostgresRow.LookupTable) {
+    init(database: PostgresDatabase, name: String, rowDescription: PostgresRow.LookupTable?) {
         self.database = database
         self.name = name
         self.rowLookupTable = rowDescription
@@ -74,6 +74,8 @@ private final class PrepareQueryRequest: PostgresRequest {
                 resultFormat: self.resultFormatCodes
             )
             return []
+        case .noData:
+            return []
         case .parseComplete, .parameterDescription:
             return []
         case .readyForQuery:
@@ -125,7 +127,10 @@ private final class ExecutePreparedQuery: PostgresRequest {
             return []
         case .dataRow:
             let data = try PostgresMessage.DataRow(message: message)
-            let row = PostgresRow(dataRow: data, lookupTable: query.rowLookupTable)
+            guard let rowLookupTable = query.rowLookupTable else {
+                fatalError("row lookup was requested but never set")
+            }
+            let row = PostgresRow(dataRow: data, lookupTable: rowLookupTable)
             try onRow(row)
             return []
         case .noData:

Tests/PostgresNIOTests/PostgresNIOTests.swift

@@ -849,6 +849,24 @@ final class PostgresNIOTests: XCTestCase {
         XCTAssertEqual(rows[2][0].column("foo")?.string, "c")
     }
 
+    // https://github.com/vapor/postgres-nio/issues/122
+    func testPreparedQueryNoResults() throws {
+        let conn = try PostgresConnection.test(on: eventLoop).wait()
+        defer { try! conn.close().wait() }
+
+        _ = try conn.simpleQuery("DROP TABLE IF EXISTS \"table_no_results\"").wait()
+        _ = try conn.simpleQuery("""
+        CREATE TABLE table_no_results (
+            "id" int8 NOT NULL,
+            "stringValue" text,
+            PRIMARY KEY ("id")
+        );
+        """).wait()
+        defer { _ = try! conn.simpleQuery("DROP TABLE \"table_no_results\"").wait() }
+
+        _ = try conn.prepare(query: "DELETE FROM \"table_no_results\" WHERE id = $1").wait()
+    }
+
 
     // https://github.com/vapor/postgres-nio/issues/71
     func testChar1Serialization() throws {