/// <summary>
/// 合并表达式 expr1 or expr2
/// 作者：李兴友
/// 日期：2020-06-08
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr1"></param>
/// <param name="expr2"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(expr1.Body);
var right = visitor.Replace(expr2.Body);
var body = Expression.OrElse(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}
/// <summary>
/// 合并表达式 expr1 AND expr2
/// 作者：李兴友
/// 日期：2020-06-08
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr1"></param>
/// <param name="expr2"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > And <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
//return expression.lambda<func<t, bool>>(expression.andalso(expr1.body, expr2.body), expr1.parameters);
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(expr1.Body);// 重新生成了一个表达式目录树
var right = visitor.Replace(expr2.Body);
var body = Expression.AndAlso(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}