LINQ条件与动态列 [英] LINQ where condition with dynamic column

问题描述

我有这个代码

// IQueryable<General> query

if (columnName == "Column1") 
{
  query = query.Where(x => x.Column1 == searchValue);
}
else if (columnName == "Column2") 
{
  query = query.Where(x => x.Column2 == searchValue);
}
else if (columnName == "Column3") 
{
  query = query.Where(x => x.Column3 == searchValue);
}
else if (columnName == "Column4") 
{
  query = query.Where(x => x.Column4 == searchValue);
}
// next zilions columns to come
// ...

我的问题是.我怎样才能将x.Column用作".Where"条件中的参数?

and my question is. How can i past x.Column as a parameter inside ".Where" condition ?

推荐答案

您可以手动创建谓词.使用此方法:

You can create a predicate manually. Use this method:

public static Expression<Func<General, bool>> CreatePredicate(string columnName, object searchValue)
{
    var xType = typeof(General);
    var x = Expression.Parameter(xType, "x");
    var column = xType.GetProperties().FirstOrDefault(p => p.Name == columnName);

    var body = column == null
        ? (Expression) Expression.Constant(true)
        : Expression.Equal(
            Expression.PropertyOrField(x, columnName),
            Expression.Constant(searchValue));

    return Expression.Lambda<Func<General, bool>>(body, x);
}

现在您可以应用谓词:

IQueryable<General> query = //
var predicate = CreatePredicate(columnName , searchValue);
query = query.Where(predicate);

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