LINQ查询以检查表中所有列中的谓词

Question

I have a table with 30 columns, and it contains 1000 rows. I want a single LINQ query, which checks for a particular value in all columns and converts the result into a list.

For example:

table.where(allcolumnvalue.contains(searchvalue)).Tolist()

How to accomplish the above using one LINQ query. Any help is much appreciated.

Answer 1

For your request all of fields should have same type, at least in the static typed C#.

The method Queriable.Where gets the Expression<Func<T, bool>> predicate as parameter. So you need build the predicate o.p1 == val || o.p2 == val || o.p3 = val ... o.p1 == val || o.p2 == val || o.p3 = val ... o.p1 == val || o.p2 == val || o.p3 = val ... as Expression value. Here o is a parameter of Expression<Func<T, bool>> :

public Expression BuildExpression<TObj, TVal>(TObj obj, TVal val)
{
    Expression<Func<TObj, bool>> predicate = (o) => o.p1 == val || ... || o.pN == val;
    return predicate;
}

but we need build predicate dynamically for all properties of TObj that have type TVal .

To simplify the code we will build equal expression false || o.p1 == val || ... || o.pN == val false || o.p1 == val || ... || o.pN == val false || o.p1 == val || ... || o.pN == val .

public Expression<Func<TObj, bool>> BuildExpression<TObj, TVal>(TVal val)
{
    var parameter = Expression.Parameter(typeof(TObj), "o");
    var valExpression = Expression.Constant(val, typeof(TVal));
    var body = Expression.Constant(false, typeof(bool));

    var properties = typeof(TObj).GetProperties()
                                 .Where(p => p.PropertyType == typeof(TVal));
    foreach (var property in properties)
    {
        var propertyExpression = Expression.Property(parameter, property);
        var equalExpression = Expression.Equal(propertyExpression, valExpression);
        body = Expression.Or(body, equalExpression);
    }

    return Expression.Lambda<Func<TObj, bool>>(body, parameter);
}

. . .

using (var dbContext = new DbContext())
{
    var whereExpression = BuildExpression<User, string>("foo");
    var contaningsFoo = dbContext.Users.Where(whereExpression);
}

Answer 2

I got answer But Is not perfect answer But Is Worked well

   public class GenericList<T>
{
    void Add(T input) { }

    public List<T> SerachFun(List<T> input, string search)
    {
        List<T> output = new System.Collections.Generic.List<T>();
        foreach (var aa in input)
        {
            var columns = aa.GetType().GetProperties().ToList();
            foreach (var bb in columns)
            {
                var cccc = bb.GetValue(aa);
                bool result = cccc.ToString().Contains(search);
                if (result)
                {
                    output.Add(aa);
                    continue;
                }

            }

        }
        return output;
    }
}

The Generic Class Object Created

        public GenericList<table1> g = new GenericList<table1>();

the Generic Class Method Called :

   var tabledetails=db.table1.ToList();
   var resultcommonsearch = g.SerachFun(tabledetails, "Dhoni");

Answer 3

using code

public class GenericList<T>
{
     public List<T> SerachFun(List<T> input, string search)
     {
            List<T> output = new System.Collections.Generic.List<T>();
            foreach (var aa in input)
            {
               var columns = aa.GetType().GetProperties().ToList();
               foreach (var bb in columns)
               {
                  var cccc = bb.GetValue(aa);
                  if(cccc!=null)
                  {
                     bool result = cccc.ToString().Contains(search);
                     if (result)
                     {
                        output.Add(aa);
                        continue;
                      }
                  }

              }

         }
            return output;
    }
  }

Try call method

 public GenericList<table1> g = new GenericList<table1>();

 var tabledetails=db.table1.ToList();
 var resultcommonsearch = g.SerachFun(tabledetails, "Dhoni");