C# 在LinqToEntities中，如何将动态列名传递给DbFunctions.Like

我在实体框架中的

DbSet

中有一个

IQueryable

。我收到一个名为

searchText

的“模糊搜索字符串”，如下所示：

public List<T> Search<T>(string searchText)
{
    using (var context = ...)
    {
        var baseQuery = context.Set<T>().AsQueryable();
        baseQuery = baseQuery.Where(x =>
            DbFunctions.Like(x.PropertyName, searchText)
            || DbFunctions.Like(x.PropertyTwo, searchText)
            || DbFunctions.Like(x.PropertyThree, searchText)
            || DbFunctio..... etc
        );
        return baseQuery.ToList();
    }
}

---

这里的问题是。。。嗯，一开始它不起作用。但主要是我没有在任何地方使用

searchText

，也不知道如何插入它。我想我很接近。。。但是我在这上面花费了大量的时间。

希望我正确地理解了您的查询逻辑：如果您想基于已知类型和列名列表构建一组类似于的条件，您可以尝试以下方法：

static private MethodInfo dbLikeMethod = typeof(DbFunctions).GetMethod(nameof(DbFunctions.Like), BindingFlags.Public | BindingFlags.Static, null, new Type[] {typeof(string), typeof(string)}, null); // I am targeting DbFunctions.Like(string, string). You might want another overload (or even mix them up depending on your inputs)

public List<T> Search<T>(string searchText) where T: class
{

    using (var context = new ...)
    {
        var baseQuery = context.Set<T>().AsQueryable().Where(CreateExpression<T>(searchText));// you could probably find a more elegant way of plugging it into your query
        return baseQuery.ToList();
    }
}

Expression<Func<T, bool>> CreateExpression<T>(string searchText) where T : class
{   
    var cols = new List<string> {
        "PropertyName",
        "PropertyTwo" // i understand you've got a way to figure out which strings you need here
    };

    var parameter = Expression.Parameter(typeof(T), "x");   
    var dbLikeCalls = cols.Select(colName => Expression.Call(dbLikeMethod, Expression.PropertyOrField(parameter, colName), Expression.Constant(searchText))); // for convenience, generate list of DbFunctions.Like(x.<Property>, searchText) expressions here
    var aggregatedCalls = dbLikeCalls.Skip(1).Aggregate((Expression)dbLikeCalls.First(), (accumulate, call) => Expression.OrElse(accumulate, call)); // aggregate the list using || operators: use first item as a seed and keep adding onto it

    return Expression.Lambda<Func<T, bool>>(aggregatedCalls, parameter);
}

static private MethodInfo dbLikeMethod=typeof（DbFunctions）.GetMethod（nameof（DbFunctions.Like），BindingFlags.Public | BindingFlags.static，null，new Type[]{typeof（string），typeof（string）}，null）；//我的目标是DbFunctions.Like（string，string）。您可能需要另一个重载（甚至根据您的输入将它们混合在一起）
公共列表搜索（字符串搜索文本），其中T:class
{
使用（var context=new…）
{
var baseQuery=context.Set（）.AsQueryable（）.Where（CreateExpression（searchText））；//您可能会找到一种更优雅的方法将其插入查询中
返回baseQuery.ToList（）；
}
}
表达式CreateExpression（字符串搜索文本），其中T:class
{   
var cols=新列表{
“PropertyName”，
“PropertyTwo”//我知道您已经找到了一种方法来确定此处需要哪些字符串
};
var参数=表达式参数（类型为（T），“x”）；
var dbLikeCalls=cols.Select（colName=>Expression.Call（dbLikeMethod，Expression.PropertyOrField（参数，colName），Expression.Constant（searchText））；//为方便起见，在此处生成DbFunctions.Like（x，searchText）表达式列表
var aggregatedCalls=dbLikeCalls.Skip（1）.Aggregate（（表达式）dbLikeCalls.First（），（累计，调用）=>Expression.OrElse（累计，调用））；//使用| |运算符聚合列表：将第一项用作种子并不断添加到其中
返回表达式.Lambda（aggregatedCalls，参数）；
}

static private MethodInfo dbLikeMethod = typeof(DbFunctions).GetMethod(nameof(DbFunctions.Like), BindingFlags.Public | BindingFlags.Static, null, new Type[] {typeof(string), typeof(string)}, null); // I am targeting DbFunctions.Like(string, string). You might want another overload (or even mix them up depending on your inputs)

public List<T> Search<T>(string searchText) where T: class
{

    using (var context = new ...)
    {
        var baseQuery = context.Set<T>().AsQueryable().Where(CreateExpression<T>(searchText));// you could probably find a more elegant way of plugging it into your query
        return baseQuery.ToList();
    }
}

Expression<Func<T, bool>> CreateExpression<T>(string searchText) where T : class
{   
    var cols = new List<string> {
        "PropertyName",
        "PropertyTwo" // i understand you've got a way to figure out which strings you need here
    };

    var parameter = Expression.Parameter(typeof(T), "x");   
    var dbLikeCalls = cols.Select(colName => Expression.Call(dbLikeMethod, Expression.PropertyOrField(parameter, colName), Expression.Constant(searchText))); // for convenience, generate list of DbFunctions.Like(x.<Property>, searchText) expressions here
    var aggregatedCalls = dbLikeCalls.Skip(1).Aggregate((Expression)dbLikeCalls.First(), (accumulate, call) => Expression.OrElse(accumulate, call)); // aggregate the list using || operators: use first item as a seed and keep adding onto it

    return Expression.Lambda<Func<T, bool>>(aggregatedCalls, parameter);
}