可能吗?
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??
解决方法
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)); }
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