可能吗？
@H_502_13@解决方法
Public String Get_Filed_By_Id(string table_Name,String Field_Name,string PK_val)
{
string strRes="";
using(mydbcontext db=new mydbcontext())
{
var x=db.table_Name.Where(p=>p.Id=PK_val).FirstOrDefault().Field_Name;
strRes=Convert.Tostring(x);
}
return strRes;
}
要么
var x=(from o in db.table_Name where o.Id=PK_val select o.Field_Name).FirstOrDefault();
在这里,我传递Table_Name,Column_Name和Condition值(PK_val)以在特定条件(Id = Pk_val)内从Table_Name获取Column_Name.
可能吗？？
Is it possible??
是的.
首先,一些帮手：
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
namespace YourNamespace
{
internal static class DbHelpers
{
public static object GetColumnById(this object dbContext,string tableName,string columnName,object id)
{
var table = (IQueryable)dbContext.GetType().GetProperty(tableName).GetValue(dbContext,null);
var row = Expression.Parameter(table.ElementType,"row");
var filter = Expression.Lambda(Expression.Equal(Expression.Property(row,"Id"),Expression.Constant(id)),row);
var column = Expression.Property(row,columnName);
var selector = Expression.Lambda(column,row);
var query = Call(Where.MakeGenericMethod(row.Type),table,filter);
query = Call(Select.MakeGenericMethod(row.Type,column.Type),query,selector);
var value = Call(FirstOrDefault.MakeGenericMethod(column.Type),query);
return value;
}
private static readonly MethodInfo Select = GetGenericMethodDefinition<
Func<IQueryable<object>,Expression<Func<object,object>>,IQueryable<object>>>((source,selector) =>
Queryable.Select(source,selector));
private static readonly MethodInfo Where = GetGenericMethodDefinition<
Func<IQueryable<object>,bool>>,object>>((source,predicate) =>
Queryable.Where(source,predicate));
private static readonly MethodInfo FirstOrDefault = GetGenericMethodDefinition<
Func<IQueryable<object>,object>>(source =>
Queryable.FirstOrDefault(source));
private static MethodInfo GetGenericMethodDefinition<TDelegate>(Expression<TDelegate> e)
{
return ((MethodCallExpression)e.Body).Method.GetGenericMethodDefinition();
}
private static object Call(MethodInfo method,params object[] parameters)
{
return method.Invoke(null,parameters);
}
}
}
现在你的功能：
public string Get_Field_By_Id(string table_Name,string field_Name,string PK_val)
{
using (var db = new mydbcontext())
return Convert.ToString(db.GetColumnById(table_Name,field_Name,PK_val));
}
