using System.Linq.Expressions;

using System.Text;

using System;

​

class Program

{

    static void Main()

    {

        var visitor = new SqlExpressionVisitor();

        string sql = visitor.TranslateToSql<Employee>(e => e.Name == "Spencer" && e.Age > 30);

        Console.WriteLine(sql);

    }

}

​

public class Employee

{

    public string Name { get; set; }

    public int Age { get; set; }

}

​

public class SqlExpressionVisitor : ExpressionVisitor

{

    private StringBuilder sb;

    private bool isWhereClauseStarted = false;

​

    public SqlExpressionVisitor()

    {

        sb = new StringBuilder();

    }

​

    public string TranslateToSql<T>(Expression<Func<T, bool>> expression)

    {

        sb.Append("SELECT * FROM ");

        sb.Append(typeof(T).Name);  // Assuming the table name is the same as the class name

        sb.Append(" WHERE ");

​

        isWhereClauseStarted = true;

        Visit(expression.Body);  // Visit the body of the lambda expression

​

        return sb.ToString();

    }

​

    protected override Expression VisitBinary(BinaryExpression node)

    {

        if (!isWhereClauseStarted)

        {

            sb.Append(" WHERE ");

            isWhereClauseStarted = true;

        }

​

        sb.Append("(");

        Visit(node.Left);

​

        switch (node.NodeType)

        {

            case ExpressionType.AndAlso:

                sb.Append(" AND ");

                break;

            case ExpressionType.Equal:

                sb.Append(" = ");

                break;

            case ExpressionType.GreaterThan:

                sb.Append(" > ");

                break;

            default:

                throw new NotSupportedException($"Operation '{node.NodeType}' is not supported");

        }

​

        Visit(node.Right);

        sb.Append(")");

​

        return node;

    }

​

    protected override Expression VisitConstant(ConstantExpression node)

    {

        if (node.Value is string)

        {

            sb.Append($"'{node.Value}'");

        }

        else

        {

            sb.Append(node.Value);

        }

​

        return node;

    }

​

    protected override Expression VisitMember(MemberExpression node)

    {

        if (node.Expression != null && node.Expression.NodeType == ExpressionType.Parameter)

        {

            sb.Append(node.Member.Name);

        }

        else

        {

            throw new NotSupportedException($"Unsupported expression part '{node}'");

        }

​

        return node;

    }

}

​