asp.net core Expression<Func<T, bool>> 类添加多个条件参数
1.直接上代码吧:注意使用的地方
expression= expression.And(p => p.Name.Equals("123"));*少了前面的的赋值只会有最后一个条件一定注意
static void Main(string[] args) { Expressionbool>> expression = null; expression = p => p.AAA.Equals(123); //expression.And(p => p.AAA==123); expression= expression.And(p => p.Name.Equals("123")); expression = expression.Or(p=>p.Age==18); Console.WriteLine("Hello World!"); }
public class Template { public int AAA { get; set; } public string Name { get; set; } public int Age { get; set; } }
public static class ExpressionBuilder { public static Expressionbool>> And ( this Expression bool>> first, Expression bool>> second) { return first.AndAlso (second, Expression.AndAlso); } public static Expression bool>> Or ( this Expression bool>> first, Expression bool>> second) { return first.AndAlso (second, Expression.OrElse); } private static Expression bool>> AndAlso (this Expression bool>> expr1, Expression bool>> expr2, Func func) { var parameter = Expression.Parameter(typeof(T)); //var parameter2 = Expression.Parameter(typeof(T)); var ddd= expr1.Parameters; var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter); var left = leftVisitor.Visit(expr1.Body); var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter);//不是用.Parameters[0]结果是不对的 var right = rightVisitor.Visit(expr2.Body); return Expression.Lambda bool>>(func(left, right), parameter); ///return Expression.Lambda(func(left, right), parameter); } private class ReplaceExpressionVisitor : ExpressionVisitor { private readonly Expression _oldValue; private readonly Expression _newValue; public ReplaceExpressionVisitor(Expression oldValue, Expression newValue) { _oldValue = oldValue; _newValue = newValue; } public override Expression Visit(Expression node) { if (node == _oldValue) return _newValue; return base.Visit(node); } } }