PostgreSQL81Dialect.cs

using System.Data;
using NHibernate.Dialect.Function;
using NHibernate.SqlCommand;

namespace NHibernate.Dialect
{
	/// <summary>
	/// An SQL dialect for PostgreSQL 8.1 and above.
	/// </summary>
	/// <remarks>
	/// <para>
	/// PostgreSQL 8.1 supports <c>FOR UPDATE ... NOWAIT</c> syntax.
	/// </para>
	/// <para>
	/// PostgreSQL supports Identity column using the "SERIAL" type.
	/// Serial type is a "virtual" type that will automatically:
	/// </para>
	/// <list type="bullet">
	/// <item><description>Create a sequence named tablename_colname_seq.</description></item>
	/// <item><description>Set the default value of this column to the next value of the 
	/// sequence. (using function <c>nextval('tablename_colname_seq')</c>)</description></item>
	/// <item><description>Add a "NOT NULL" constraint to this column.</description></item>
	/// <item><description>Set the sequence as "owned by" the table.</description></item>
	/// </list>
	/// <para>
	/// To insert the next value of the sequence into the serial column,
	/// exclude the column from the list of columns 
	/// in the INSERT statement or use the DEFAULT key word.
	/// </para>
	/// <para>
	/// If the table or the column is dropped, the sequence is dropped too.
	/// </para>
	/// </remarks>
	/// <seealso cref="PostgreSQLDialect" />
	public class PostgreSQL81Dialect : PostgreSQLDialect
	{
		protected override void RegisterDateTimeTypeMappings()
		{
			base.RegisterDateTimeTypeMappings();
			RegisterColumnType(DbType.DateTime, 6, "timestamp($s)");
			RegisterColumnType(DbType.Time, 6, "time($s)");
			// Not overriding default scale: Posgres doc writes it means "no explicit limit", so max of what it can support,
			// which suits our needs.

			// timezone seems not available prior to version 8.0
			RegisterFunction(
				"current_utctimestamp",
				new SQLFunctionTemplate(NHibernateUtil.UtcDateTime, "timezone('UTC', current_timestamp)"));
		}

		public override string ForUpdateNowaitString
		{
			get { return " for update nowait"; }
		}

		public override string GetForUpdateNowaitString(string aliases)
		{
			return " for update of " + aliases + " nowait";
		}

		/// <summary>
		/// PostgreSQL supports Identity column using the "SERIAL" type.
		/// </summary>
		public override bool SupportsIdentityColumns
		{
			get { return true; }
		}

		/// <summary>
		/// PostgreSQL doesn't have type in identity column.
		/// </summary>
		/// <remarks>
		/// To create an identity column it uses the SQL syntax
		/// <c>CREATE TABLE tablename (colname SERIAL);</c> or 
		/// <c>CREATE TABLE tablename (colname BIGSERIAL);</c>
		/// </remarks>
		public override bool HasDataTypeInIdentityColumn
		{
			get { return false; }
		}

		/// <summary>
		/// PostgreSQL supports <c>serial</c> and <c>serial4</c> type for 4 bytes integer auto increment column.
		/// <c>bigserial</c> or <c>serial8</c> can be used for 8 bytes integer auto increment column.
		/// </summary>
		/// <returns><c>bigserial</c> if <paramref name="type"/> equal Int64,
		/// <c>serial</c> otherwise</returns>
		public override string GetIdentityColumnString(DbType type)
		{
			return (type == DbType.Int64) ? "bigserial" : "serial";
		}

		/// <summary>
		/// The sql syntax to insert a row without specifying any column in PostgreSQL is
		/// <c>INSERT INTO table DEFAULT VALUES;</c>
		/// </summary>
		public override string NoColumnsInsertString
		{
			get { return "default values"; }
		}

		/// <summary>
		/// PostgreSQL 8.1 and above defined the function <c>lastval()</c> that returns the
		/// value of the last sequence that <c>nextval()</c> was used on in the current session.
		/// Call <c>lastval()</c> if <c>nextval()</c> has not yet been called in the current
		/// session throw an exception.
		/// </summary>
		public override string IdentitySelectString
		{
			get { return "select lastval()"; }
		}

		public override SqlString AppendIdentitySelectToInsert(SqlString insertSql)
		{
			return insertSql.Append("; " + IdentitySelectString);
		}

		public override SqlString AppendIdentitySelectToInsert(SqlString insertString, string identifierColumnName)
		{
			return insertString.Append(" returning ", identifierColumnName);
		}

		public override bool SupportsInsertSelectIdentity
		{
			get { return true; }
		}

		/// <inheritdoc />
		public override bool SupportsDateTimeScale => true;

		// Said to be 63 bytes at least since v8.
		/// <inheritdoc />
		public override int MaxAliasLength => 63;
	}
}