/// <summary>
/// 访问 <see cref="T:System.Linq.Expressions.BinaryExpression"/> 的子级。
/// </summary>
/// <returns>
/// 如果修改了该表达式或任何子表达式，则为修改后的表达式；否则返回原始表达式。
/// </returns>
/// <param name="binaryExpression">要访问的表达式。</param>
protected override Expression VisitBinary(BinaryExpression binaryExpression)
{
Check.NotNull(binaryExpression, nameof(binaryExpression));
if (binaryExpression.NodeType == ExpressionType.Coalesce)
{
Sql.Append("COALESCE(");
Visit(binaryExpression.Left);
Sql.Append(", ");
Visit(binaryExpression.Right);
Sql.Append(")");
}
else
{
var needParentheses
= !binaryExpression.Left.IsSimpleExpression() ||
!binaryExpression.Right.IsSimpleExpression() ||
binaryExpression.IsLogicalOperation();
if (needParentheses)
{
Sql.Append("(");
}
Visit(binaryExpression.Left);
if (binaryExpression.IsLogicalOperation() &&
binaryExpression.Left.IsSimpleExpression())
{
Sql.Append(" = ");
Sql.Append(_sqlHelper.EscapeLiteral(true));
}
if (!TryGenerateBinaryOperator(binaryExpression.NodeType, out var op))
{
throw new ArgumentOutOfRangeException();
}
if ((binaryExpression.NodeType == ExpressionType.NotEqual ||
binaryExpression.NodeType == ExpressionType.Equal) &&
binaryExpression.Right.NodeType == ExpressionType.Constant)
{
var value = binaryExpression.Right.Invoke();
if (value == null)
{
Sql.Append(binaryExpression.NodeType == ExpressionType.Equal
? " IS NULL "
: " IS NOT NULL ");
}
else
{
Sql.Append(op);
Sql.Append(_sqlHelper.EscapeLiteral(value));
}
}
else
{
Sql.Append(op);
Visit(binaryExpression.Right);
if (binaryExpression.IsLogicalOperation() &&
binaryExpression.Right.IsSimpleExpression())
{
Sql.Append(" = ");
Sql.Append(_sqlHelper.EscapeLiteral(true));
}
}
if (needParentheses)
{
Sql.Append(")");
}
}
return(binaryExpression);
}
/// <summary> /// 格式化SQL查询字符串。 /// </summary> /// <param name="value">值对象。</param> /// <returns>返回格式化后的字符串。</returns> protected string Escape(object value) => SqlHelper.EscapeLiteral(value);