C# SQL 查詢物件化：建構型別安全的動態查詢建構器

動機

字串拼湊 SQL 易錯、難維護、有注入風險。將查詢條件**物件化**，以流暢介面 (Fluent API) 建構 WHERE 子句，再由建構器產生參數化 SQL，兼顧型別安全、可讀性與效能。

核心介面設計

public interface IExpression
{
    /// 
產生 WHERE 片段 (含參數佔位符)
    string GetFilter(IDriverType driver);

    /// 
取得對應參數陣列
    IDataParameter[] GetParameters(IDriverType driver);

    /// 
組合子表達式 (AND/OR)
    void Add(LogicOperator op, params IExpression[] expressions);
    void Add(params IExpression[] expressions); // 預設 AND
}

public enum LogicOperator { And, Or }

public interface IDriverType
{
    string FormatParameterName(string baseName, string sequence); // e.g. @Name_0
    IDataParameter CreateParameter(string name, object value);
}

基礎實作：複合表達式

[Serializable]
public abstract class ExpressionBase : IExpression
{
    private readonly List _children = new();
    private readonly List _operators = new(); // 與 _children 對應，第一個通常忽略
    public string Sequence { get; set; } = "";

    public void Add(LogicOperator op, params IExpression[] expressions)
    {
        foreach (var exp in expressions ?? Array.Empty())
        {
            if (exp == null) continue;
            exp.Sequence = Sequence + _children.Count;
            _operators.Add(op);
            _children.Add(exp);
        }
    }

    public void Add(params IExpression[] expressions) => Add(LogicOperator.And, expressions);

    public virtual string GetFilter(IDriverType driver)
    {
        if (_children.Count == 0) return "1=1";

        var sb = new StringBuilder();
        for (int i = 0; i < _children.Count; i++)
        {
            string op = i == 0 ? "" : (_operators[i] == LogicOperator.And ? " AND " : " OR ");
            sb.Append(op).Append('(').Append(_children[i].GetFilter(driver)).Append(')');
        }
        return sb.ToString();
    }

    public virtual IDataParameter[] GetParameters(IDriverType driver)
    {
        var list = new List();
        foreach (var child in _children)
        {
            var ps = child.GetParameters(driver);
            if (ps != null) list.AddRange(ps);
        }
        return list.ToArray();
    }
}

葉節點表達式：比較運算子

public abstract class CompareExpression : ExpressionBase
{
    public string ColumnName { get; set; }
    public object Value { get; set; }

    protected CompareExpression(string column, object value)
    {
        ColumnName = column;
        Value = value;
    }

    protected abstract string OperatorSymbol { get; } // =, <>, >, <, >=, <=, LIKE, IN, NOT IN

    public override string GetFilter(IDriverType driver)
    {
        string paramName = driver.FormatParameterName(ColumnName, Sequence);
        return $"{ColumnName} {OperatorSymbol} {paramName}";
    }

    public override IDataParameter[] GetParameters(IDriverType driver)
    {
        return new[] { driver.CreateParameter(driver.FormatParameterName(ColumnName, Sequence), Value) };
    }
}

// 具體比較類別
public sealed class EqualExpression : CompareExpression
{
    public EqualExpression(string column, object value) : base(column, value) { }
    protected override string OperatorSymbol => "=";
}

public sealed class NotEqualExpression : CompareExpression { /* <> */ }
public sealed class GreaterThanExpression : CompareExpression { /* > */ }
public sealed class LessThanExpression : CompareExpression { /* < */ }
public sealed class LikeExpression : CompareExpression { /* LIKE */ }
public sealed class InExpression : CompareExpression
{
    public InExpression(string column, IEnumerable