使用PredicateBuilder构建跨多个实体列的查询搜索 [英] Using PredicateBuilder to build query searching across multiple columns of Entity

问题描述

我有一个字段名列表.我正在尝试建立一个谓词，以查看字段中是否包含搜索词.我已经完成了

I have a list of field names. I am trying to build a predicate to look in the fields to see if they contain the search term. I have gone done the path listed in this original question but do not understand how to do a Contains instead of a NotEqual.

string searchTerm = "Fred";    
foreach (var field in FieldNames)
{
    myPredicate= myPredicate.And(m => m.*field*.Contains(searchTerm));                    
} 

到目前为止，我的代码:

My code so far:

public static Expression<Func<T, bool>> MultiColumnSearchExpression<T>(string fieldName,string searchValue)
{
    var parameter = Expression.Parameter(typeof(T), "m");
    var fieldAccess = Expression.PropertyOrField(parameter, fieldName);
   //this next line should do a Contains rather then NotEqual but how?
    var body = Expression.NotEqual(fieldAccess, nullValue);

    var expr = Expression.Lambda<Func<T, bool>>(body, parameter);
    return expr;
}

推荐答案

所以您想致电

So you want to call String.Contains method.

这是具有以下签名的String类 instance 方法

It is a String class instance method with the following signature

public bool Contains(string value)

可以映射到以下Expression.Call 这是方法:

public static Expression<Func<T, bool>> ContainsPredicate<T>(string memberName, string searchValue)
{
    var parameter = Expression.Parameter(typeof(T), "m");
    var member = Expression.PropertyOrField(parameter, memberName);
    var body = Expression.Call(
        member,
        "Contains",
        Type.EmptyTypes, // no generic type arguments
        Expression.Constant(searchValue)
    );    
    return Expression.Lambda<Func<T, bool>>(body, parameter);
}

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