SqlExpressionVisitor.cs - main - Frexto/frexto-orm

SqlExpressionVisitor.cs
67 строк2 KB
Maksim Fomin
orm
07 окт 2025, 10:58
07 окт 2025, 10:58f4c0f72
using System.Linq.Expressions;
using System.Text;

namespace FrextoORM;

public class SqlExpressionVisitor : ExpressionVisitor
{
    private readonly StringBuilder _sql = new();
    private readonly List<object> _parameters = [];
    
    public (string sql, object[] parameters) Translate(Expression expr)
    {
        Visit(expr);
        return (_sql.ToString(), _parameters.ToArray());
    }

    protected override Expression VisitBinary(BinaryExpression node)
    {
        _sql.Append("(");
        Visit(node.Left);

        switch (node.NodeType)
        {
            case ExpressionType.Equal:        _sql.Append(" = "); break;
            case ExpressionType.NotEqual:     _sql.Append(" <> "); break;
            case ExpressionType.GreaterThan:  _sql.Append(" > "); break;
            case ExpressionType.GreaterThanOrEqual: _sql.Append(" >= "); break;
            case ExpressionType.LessThan:     _sql.Append(" < "); break;
            case ExpressionType.LessThanOrEqual: _sql.Append(" <= "); break;
            case ExpressionType.AndAlso:      _sql.Append(" AND "); break;
            case ExpressionType.OrElse:       _sql.Append(" OR "); break;
            default:
                throw new NotSupportedException($"Оператор {node.NodeType} не поддерживается");
        }
        
        Visit(node.Right);
        _sql.Append(")");
        return node;
    }

    protected override Expression VisitMember(MemberExpression node)
    {
        if (node.Expression?.NodeType == ExpressionType.Parameter)
        {
            _sql.Append(node.Member.Name.ToLower());
            return node;
        }

        var value = GetValue(node);
        AddParameter(value);
        return node;
    }

    private void AddParameter(object value)
    {
        var paramName = $"@p{_parameters.Count}";
        _sql.Append(paramName);
        _parameters.Add(value);
    }

    private object GetValue(MemberExpression member)
    {
        var objectMember = Expression.Convert(member, typeof(object));
        var lambda = Expression.Lambda<Func<object>>(objectMember);
        return lambda.Compile().Invoke();
    }
}