I want to write a query in .net core using ef. Now the issue is, I am getting the property name in parameter and I want to put condition on that property ie
public IQueryable<MyModel> Generate(string property, IQueryable<MyModel> query)
{
query = query.Where(a => a.property.ToLower() != null);
}
MyModel:
public string Property1 { get; set; }
public string Property2 { get; set; }
public string Property3 { get; set; }
Method Calling:
var query = Generate(MyModel.Property2, query);
I know this is possible using reflection but that has some performance impacts. So is there any better approach?
Can you use Func<MyModel, string>
as param?
public IQueryable<MyModel> Generate(Func<MyModel, string> propertySelector, IQueryable<MyModel> query)
{
query = query.Where(a => propertySelctor(a).ToLower() != null);
}
And use like:
var query = Generate(m => m.Property2, query);
EDIT after question clarification:
You could implement a generic extension method for IQueryable where the clause is dynamically built:
public static class QueryExtensions
{
public static IQueryable<TModel> WhereNotNull<TModel>(this IQueryable<TModel> query, string propertyName)
{
var parameter = Expression.Parameter(typeof(TModel), "x");
var body = Expression.PropertyOrField(parameter, propertyName);
var comparison = Expression.NotEqual(body, Expression.Constant(null, typeof(object)));
var lambda = Expression.Lambda<Func<TModel, bool>>(comparison, parameter);
return query.Where(lambda);
}
}
Call it like:
query = query.WhereNotNull(nameof(MyModel.Property1));
or
query = query.WhereNotNull("Property1");
EDIT after request for null or whitespace check on strings:
Example of calling string.IsNullOrWhiteSpace()
on string properties:
public static IQueryable<TModel> WhereNotNull<TModel>(this IQueryable<TModel> query, string propertyName)
{
var parameter = Expression.Parameter(typeof(TModel), "x");
var body = Expression.PropertyOrField(parameter, propertyName);
Expression<Func<TModel, bool>> lambda = null;
if (body.Type == typeof(string))
{
var methodCall = Expression.Call(typeof(string), nameof(string.IsNullOrWhiteSpace), null, body);
var nullOrWhiteSpaceComparison = Expression.Not(methodCall);
lambda = Expression.Lambda<Func<TModel, bool>>(nullOrWhiteSpaceComparison, parameter);
}
else
{
var nullComparison = Expression.NotEqual(body, Expression.Constant(null, typeof(object)));
lambda = Expression.Lambda<Func<TModel, bool>>(nullComparison, parameter);
}
return query.Where(lambda);
}
If you (in some other context) want to combine multiple expressions you may use Expression.And(Expression left, Expression right)
or Expression.Or(Expression left, Expression right)
. Pass the unary/binary expression as parameters left and right.
You can do it like this:
public IQueryable<TModel> Generate<TModel, TProperty>(Func<TModel, TProperty> propertyFunc, IQueryable<TModel> query)
{
return query.Where(a => propertyFunc(a) != null);
}
It will be a more flexible solution than Dmitry.
public IQueryable<MyModel> Generate(string property, IQueryable<MyModel> query)
{
query = query.Where(a => EF.Property<string>(a, property) != null);
}
Reference: EF.Property(Object, String) Method
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