I have a .net 8 project with Entity Framework and I want to build a dynamic query for it.
User can define columns based by his choices using existing tables:
For example:
I have 3 tables: Divisions
, Industries
, Portfolios
, and a fourth table EntryLine
which is related to those 3.
In the UI user has a list of 3 columns which he could choose:
Division, Industry, Portfolio
. He can choose any combination of those 3, for example only 2 of them, only one etc.
Based on what user will choose I need to create this:
var entryLines = _context.EntryLines.AsQueryable();
Expression<Func<EntryLine, object>> func;
if(user choosed divizion){
func.Append(x => new { DivisionName = x.EntryLine.Division.Name});
// func = new {x.EntryLine.Division.Name};
}
if (user chose industry) {
func.Append(x => new { IndustryName = x.EntryLine.Industry.Name });
// if user did NOT choose industry - func = new { DivisionName = x.EntryLine.Division.Name};
// if user chose industry -
// func = new {
// DivisionName = x.EntryLine.Division.Name
// IndustryName = x.EntryLine.Industry.Name
// };
}
After that call:
entryLines.GroupBy(func);
and so on..
I give you a simple example, but I have more columns, and a much much complex database, but the main idea is to create a single anonymous object based on what user chose in the UI and pass it to the GroupBy linq and also select the data and so on.
I found the solution with reflection and functional programing
public static class ExpressionHelper
{
public static Func<Tin, object> BuildPredicate<Tin>(params string[] propertyNames)
{
var parameter = Expression.Parameter(typeof(Tin), "x");
List<Expression> propertyExpressions = new List<Expression>();
foreach (var propertyName in propertyNames)
{
PropertyInfo propertyInfo = typeof(Tin).GetProperty(propertyName);
if (propertyInfo == null)
{
throw new InvalidOperationException($"No property with name {propertyName} found.");
}
MemberExpression propertyAccess = Expression.PropertyOrField(parameter, propertyName);
propertyExpressions.Add(Expression.Convert(propertyAccess, typeof(object)));
}
MethodInfo tupleCreateMethod = typeof(ValueTuple).GetMethods()
.First(m => m.Name == "Create" && m.GetParameters().Length == propertyNames.Length);
var genericTupleCreateMethod = tupleCreateMethod.MakeGenericMethod(propertyExpressions.Select(e => e.Type).ToArray());
var tupleCreation = Expression.Call(genericTupleCreateMethod, propertyExpressions);
var boxedTuple = Expression.Convert(tupleCreation, typeof(object));
LambdaExpression lambda = Expression.Lambda(typeof(Func<Tin, object>), boxedTuple, parameter);
return (Func<Tin, object>)lambda.Compile();
}
}
the call will be:
groupByColumns will be a list of strings like ["column1", column2 etc]
var groupByPredicate = ExpressionHelper.BuildPredicate<EntryLineDetailedDto>(groupByColumns);
var groupedEntryLines = entryLinesQuery.GroupBy(groupByPredicate)
.Skip((pageNumber - 1) * pageSize)
.Take(pageSize).ToList();