如何建立这种复杂的LINQ表达？ [英] How to build this complex Linq expression?

问题描述

我要从字符串List 构建一个System.Linq.Expression

I want to build a System.Linq.Expression from the string List like this:

System.Linq.Expressions.Expression x = null;

foreach (string s in GetWords(input))
{
    /* Create Expression */
}

所以我可以使用：

.Where(x =>
         x.Name.Like(string.Format("%{0}%", word1)) ||
         x.Name.Like(string.Format("%{0}%", word2)) ||
         x.Name.Like(string.Format("%{0}%", word3)) ||
         x.Id.ToString().Like(string.Format("%{0}%", word1)) ||
         x.Id.ToString().Like(string.Format("%{0}%", word2)) ||
         x.Id.ToString().Like(string.Format("%{0}%", word3)) ||
       );

x is MyObject

推荐答案

类似：

string[] words = { "foo", "bar", "blop" }; // your data

Expression body = null;
var param = Expression.Parameter(typeof(SomeType), "x");
var id = Expression.PropertyOrField(param, "Id");
var name = Expression.PropertyOrField(param, "Name");
foreach (string word in words)
{
    var wordExpr = Expression.Constant(word, typeof(string));
    var wordTest = Expression.OrElse(
        Expression.Call(id, "Contains", null, wordExpr),
        Expression.Call(name, "Contains", null, wordExpr));
    body = body == null ? wordTest : Expression.OrElse(body, wordTest);
}
Expression<Func<SomeType,bool>>lambda;
if (body == null) { lambda = x => false; }
else { lambda = Expression.Lambda<Func<SomeType, bool>>(body, param); }

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