FreeSql之Expression表达式拼接参数扩展

在FreeSql源码中Expression表达式拼接默认最多支持到5个泛型参数，当我们使用表关联比较多的时候，就需要进行扩展。



新建一个类，将命名空间改为System.Linq.Expressions，并加入参数扩展

namespace System.Linq.Expressions
{
    static partial class LambadaExpressionExtensions
    {
	//如需扩展增加泛型参数即可
        #region T1, T2, T3, T4, T5 ,T6
        /// <summary>
        /// 使用 and 拼接两个 lambda 表达式
        /// </summary>
        /// <returns></returns>
        public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> And<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => And(exp1, true, exp2);
        /// <summary>
        /// 使用 and 拼接两个 lambda 表达式
        /// </summary>
        /// <param name="exp1"></param>
        /// <param name="condition">true 时生效</param>
        /// <param name="exp2"></param>
        /// <returns></returns>
        public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> And<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, bool condition, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => (Expression<Func<T1, T2, T3, T4, T5, T6, bool>>)InternalAndOrExpression(condition, exp1, exp2, true);
        /// <summary>
        /// 使用 or 拼接两个 lambda 表达式
        /// </summary>
        /// <returns></returns>
        public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> Or<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => Or(exp1, true, exp2);
        /// <summary>
        /// 使用 or 拼接两个 lambda 表达式
        /// </summary>
        /// <param name="exp1"></param>
        /// <param name="condition">true 时生效</param>
        /// <param name="exp2"></param>
        /// <returns></returns>
        public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> Or<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp1, bool condition, Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp2) => (Expression<Func<T1, T2, T3, T4, T5, T6, bool>>)InternalAndOrExpression(condition, exp1, exp2, false);
        /// <summary>
        /// 将 lambda 表达式取反
        /// </summary>
        /// <param name="exp"></param>
        /// <param name="condition">true 时生效</param>
        /// <returns></returns>
        public static Expression<Func<T1, T2, T3, T4, T5, T6, bool>> Not<T1, T2, T3, T4, T5, T6>(this Expression<Func<T1, T2, T3, T4, T5, T6, bool>> exp, bool condition = true) => (Expression<Func<T1, T2, T3, T4, T5, T6, bool>>)InternalNotExpression(condition, exp);
        #endregion
        #region 通用表达式方法
        static LambdaExpression InternalAndOrExpression(bool condition, LambdaExpression exp1, LambdaExpression exp2, bool isAndAlso)
        {
            if (condition == false) return exp1;
            if (exp1 == null) return exp2;
            if (exp2 == null) return exp1;
            var newParameters = exp1.Parameters.Select((a, b) => Expression.Parameter(a.Type, a.Name /*$"new{b}"*/)).ToArray();
            var left = new NewExpressionVisitor(newParameters, exp1.Parameters.ToArray()).Replace(exp1.Body);
            var right = new NewExpressionVisitor(newParameters, exp2.Parameters.ToArray()).Replace(exp2.Body);
            var body = isAndAlso ? Expression.AndAlso(left, right) : Expression.OrElse(left, right);
            return Expression.Lambda(exp1.Type, body, newParameters);
        }
        static LambdaExpression InternalNotExpression(bool condition, LambdaExpression exp)
        {
            if (condition == false) return exp;
            if (exp == null) return null;
            var newParameters = exp.Parameters.Select((a, b) => Expression.Parameter(a.Type, a.Name /*$"new{b}"*/)).ToArray();
            var body = Expression.Not(exp.Body);
            return Expression.Lambda(exp.Type, body, newParameters);
        }
        internal class NewExpressionVisitor : ExpressionVisitor
        {
            ParameterExpression[] _newParameters;
            ParameterExpression[] _oldParameters;
            public NewExpressionVisitor(ParameterExpression newParam, ParameterExpression oldParam) : this(new[] { newParam }, new[] { oldParam }) { }
            public NewExpressionVisitor(ParameterExpression[] newParams, ParameterExpression[] oldParams)
            {
                this._newParameters = newParams;
                this._oldParameters = oldParams;
            }
            public Expression Replace(Expression exp) => this.Visit(exp);
            protected override Expression VisitParameter(ParameterExpression node)
            {
                for (var a = 0; a < _oldParameters.Length; a++)
                    if (_oldParameters[a] == node)
                        return _newParameters[a];
                return node;
            }
        }
        #endregion
    }
}

以上代码是将表达式拼接扩展至6个泛型参数，以此类推。

因为属于同一个命名空间，可以直接使用。