C＃动态表达式树使用Where（或Any）和泛型

目前，我有一个可用的帮助函数，它创建一个简单的表达式来搜索一个通用实体（TEntity）以获得搜索项（单个词/短语）。它创建下面的表达式：C＃动态表达式树使用Where（或Any）和泛型

q => q.Product.ProductTitle.Contains(searchText: 'red shirt')

我只需要扩展该助手来搜索每个字包括在搜索项（例如SEARCHTEXT：“红色衬衫” - > searchTerms：[“红”，“衬衫” ]）

var searchTerms = searchText.ToLower().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList(); 
searchTerms.Any(s => !q.Product.ProductTitle.ToLower().Contains(s))

函数列在下面 - 我已经评论了需要完成的代码。

public static Expression<Func<TEntity, bool>> CreateSearchQuery(List<PropertyInfo> searchPropertiesList, string searchText, SearchType searchType = SearchType.Contains) 
    { 
     if(string.IsNullOrWhiteSpace(searchText) || searchPropertiesList == null || searchPropertiesList.Count <= 0) 
     { 
      return null; 
     } 

     var searchTerms = searchText.ToLower().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList(); 
     var searchExpressionList = new List<Expression<Func<TEntity, bool>>>(); 
     foreach(var property in searchPropertiesList.Where(x => x.GetCustomAttributes(false).Any(c => c.GetType() != typeof(NotMappedAttribute)))) 
     { 
      //search param 
      var searchParam = Expression.Parameter(typeof(string), "s"); 

      //search type 
      var searchTypeMethod = typeof(string).GetMethod(searchType.ToString(), new[] { typeof(string) }); 

      //entity expression. 
      var entityParam = Expression.Parameter(typeof(TEntity), "q"); 
      var entityProperty = Expression.Property(entityParam, property); 
      var entityExpression = Expression.Call(
       Expression.Call(entityProperty, typeof(string).GetMethod("ToLower", System.Type.EmptyTypes)), 
       searchTypeMethod, 
       Expression.Call(searchParam, typeof(string).GetMethod("ToLower", System.Type.EmptyTypes)) 
      ); 
      var entityPredicateBody = Expression.Lambda<Func<TEntity, bool>>(entityExpression, entityParam); 

      ////TODO: CONSIDER EACH TERM AND CREATE WHERE/ANY EXPRESSION 
      //searchTerms.Any(s => !q.Product.ProductTitle.ToLower().Contains(s)) 
      //var filterExpression = Expression.Call(
      // typeof(Enumerable), 
      // "Where", 
      // new[] { typeof(TEntity) }, 
      // searchParam, 
      // entityPredicateBody); 
      //var expressionBody = Expression.Lambda<Func<TEntity, bool>>(filterExpression, searchParam); 

      //TODO: REPLACE WITH NEW EXPRESSION (expressionBody) 
      searchExpressionList.Add(entityPredicateBody); 
     }

来源

2017-04-18 Steve McCormack

为什么你有用单引号（''红衬衫'）包裹的字符串？如果你想能够扩展它来接受多个字符串，你可以使用它作为你的函数参数：'（List searchPropertiesList，SearchType searchType，params string [] args）'，那么你只需要处理传入的1个（或更多）'args'。请参阅：https：//msdn.microsoft.com/en-us/library/w5zay9db.aspx –

感谢您的反馈Zac。我会在未来更新或改变行为。 –

它应该是：

public static Expression<Func<TEntity, bool>> CreateSearchQuery<TEntity>(List<PropertyInfo> properties, string text, SearchType searchType = SearchType.Contains) 
{ 
    if (string.IsNullOrWhiteSpace(text) || properties == null || properties.Count == 0) 
    { 
     return null; 
    } 

    // For comparison 
    //Expression<Func<ProductContainer, bool>> exp = q => searchText.Any(x => q.Product.ProductTitle.ToLower().Contains(x)); 

    var expressions = new List<Expression>(); 

    var entity = Expression.Parameter(typeof(TEntity), "q"); 

    //search type 
    var searchMethod = typeof(string).GetMethod(searchType.ToString(), new[] { typeof(string) }); 

    //search terms 
    var searchTerms = Expression.Constant(text.ToLower().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)); 

    //search param 
    var str = Expression.Parameter(typeof(string), "s"); 

    foreach (var property in properties.Where(
     x => x.GetCustomAttribute<NotMappedAttribute>() == null)) 
    { 
     var entityProperty = Expression.Property(entity, property); 
     var toLower = Expression.Call(entityProperty, "ToLower", Type.EmptyTypes); 
     var contains = Expression.Call(toLower, searchMethod, str); 

     var anyExpression = Expression.Lambda<Func<string, bool>>(contains, str); 

     var any = Expression.Call(typeof(Enumerable), "Any", new[] { typeof(string) }, searchTerms, anyExpression); 

     expressions.Add(any); 
    } 

    var ors = expressions.Aggregate((x, y) => Expression.Or(x, y)); 

    var exp = Expression.Lambda<Func<TEntity, bool>>(ors, entity); 
    return exp; 
}

我已经把所有or是由不同的特性（Aggregate附近的方法结束）所产生的各种表情。

来源

2017-04-19 07:24:09 xanatos

C＃动态表达式树使用Where（或Any）和泛型

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