I'm trying to run a custom query in my repository, but I'm getting a InvalidDataAccessResourceUsageException. "Don't know how to treat that as a predicate String("n.id = '1234'")".
public void myMethod() {
myRepository.queryUsingCustomFilters("n.id = '1234'");
}
public interface MyRepository() extends Neo4jRepository<MyObject, String> {
#Query("MATCH (n) WHERE {filter} RETURN n")
List<MyObject> queryUsingCustomFilters(#Param("filter") String filter);
}
I have a simple example for now, but the string I'm passing in the future could be a little bit more complicated, such as "n.id = '1234' AND (n.name = 'one name' OR n.name = 'another name')"
I don't believe you can pass entire clauses/predicates/queries as a #Param.
If you want to build queries at run time, you might want to look at composing it using the lower level Neo4j OGM filters (see https://neo4j.com/docs/ogm-manual/current/reference/#reference:filters)
So in the case you describe above, you could simply add Filters as required and chain them together to build your WHERE clause
Related
Trying to search for users details by using userid,emailid,firstname,lastname,GUID,etc...many more values that need to be added in future
The search should be performed using all the attributes which are not null.
Found this piece of code online *
String filter = "(&(sn=YourName)(mail=*))";
*
Is there any other predefined template or such to do the search, more optimal way without directly specifying values to be Null or using if else statements for each and every attribute? All values must be passed to the method and those not null must be used for search using LDAP. Anything? Please help.
You can effectively use the Filters at run time to specify what to use for search and what not depending on some rules or your NULL validations on attributes. Pls find sample code which fetches person name using filters in ldapTemplate :-
public static final String BASE_DN = "dc=xxx,dc=yyy";
private LdapTemplate ldapTemplate ;
public List getPersonNames() {
String cn = "phil more";
String sn = "more";
AndFilter filter = new AndFilter();
filter.and(new EqualsFilter("objectclass", "person"));
filter.and(new EqualsFilter("sn", sn));
filter.and(new WhitespaceWildcardsFilter("cn", cn));
return ldapTemplate.search(
BASE_DN,
filter.encode(),
new AttributesMapper() {
public Object mapFromAttributes(Attributes attrs)
throws NamingException {
return attrs.get("cn").get();
}
});
}
As name suggests the AndFilters joins all individual filters used in lookup like EqualFilter which checks for equality of attributes while WhitespaceWildcardsFilter to perform wildcard search. So here like we got cn = phil more, it in turn uses *phil*more* for search.
I am creating a repository that using entity framework (also domain objects) and I need to query all records that does not contain value "BADGE/" (undesired value). I found a method that is ".Contains", but cannot find something equivalent to "notContains" or way to exclude records that have the undesired value. I would like the replace "p.Lname.Contains("BADGE/") with something like "p.Lname.NotContains("BADGE/") or something like that where it excludes the values during the return. Here is what I have so far:
public IQueryable<Personnel> NoBadgePersonnels
{
get {
return Context.Personnels.Where(p => p.Lname.Contains("BADGE/"));
}
}
additionally, this what my context looks like:
public class EmployeeRepository
{
private readonly EFContextProvider<EmployeeDbContext>
_contextProvider = new EFContextProvider<EmployeeDbContext>();
private EmployeeDbContext Context
{
get { return _contextProvider.Context; }
}
thanks community
Nick
Try:
return Context.Personnels.Where(p => p.Lname.IndexOf("BADGE/") == -1);
This excludes any strings which contain your target string.
I know there is a way to use Expressions and Lambdas to accomplish this but I having a hard time piecing it all together. All I need is a method that will dynamically query an Entity Framework DBSet object to find the row where the propery with the given name matches the value.
My context:
public class MyContext : DbContext
{
public IDbSet<Account> Accoounts{ get { return Set<Account>(); } }
}
The method that I'm looking to write:
public T Get<T>(string property, object value) : where T is Account
{...}
I would rather not have to use Dynamic SQL to accomplish this so no need to suggest it because I already know it's possible. What I'm really looking for is some help to accomplish this using Expressions and Lambdas
Thanks in advance, I know it's brief but it should be pretty self-explanatory. Comment if more info is needed
I'm trying to avoid dynamic linq as much as possible because the main point of linq is strongly typed access. Using dynamic linq is a solution but it is exactly the oppose of the linq purpose and it is quite close to using ESQL and building the query from sting concatenation. Anyway dynamic linq is sometimes real time saver (especially when it comes to complex dynamic ordering) and I successfully use it in a large project with Linq-to-Sql.
What I usually do is defining some SearchCriteria class like:
public class SearchCriteria
{
public string Property1 { get; set; }
public int? Property2 { get; set; }
}
And helper query extension method like:
public static IQueryable<SomeClass> Filter(this IQueryable<SomeClass> query, SearchCriteria filter)
{
if (filter.Property1 != null) query = query.Where(s => s.Property1 == filter.Property1);
if (filter.Property2 != null) query = query.Where(s => s.Property2 == filter.Property2);
return query;
}
It is not generic solution. Again generic solution is for some strongly typed processing of classes sharing some behavior.
The more complex solution would be using predicate builder and build expression tree yourselves but again building expression tree is only more complex way to build ESQL query by concatenating strings.
Here's my implementation:
public T Get<T>(string property, object value) : where T is Account
{
//p
var p = Expression.Parameter(typeof(T));
//p.Property
var propertyExpression = Expression.Property(p, property);
//p.Property == value
var equalsExpression = Expression.Equal(propertyExpression, Expression.Constant(value));
//p => p.Property == value
var lambda = Expression.Lambda<Func<T,bool>>(equalsExpression, p);
return context.Set<T>().SingleOrDefault(lambda);
}
It uses EF 5's Set<T>() method. If you are using a lower version, you'll need to implement a way of getting the DbSet based on the <T> type.
Hope it helps.
Dynamic Linq may be an option. Specify your criteria as a string and it will get built as an expression and ran against your data;
An example from something I have done;
var context = new DataContext(ConfigurationManager.ConnectionStrings["c"].ConnectionString);
var statusConditions = "Status = 1";
var results = (IQueryable)context.Contacts.Where(statusConditions);
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
i separated my application into a DAL, BL, UI.
I used entity framework code first throw repositories to access the sql database.
public class Person{
...
}
public class PersonRepository{
Create(...){...}
Update(...){...}
Delete(...){...}
GetById(...){...}
Query(...){...}
...
Now the thing is the BL i'm working on a method to get all the Persons who are leaving near an adress
public GetPersonsNear(string Address){
...
}
private bool AddressesAreClose(string address1, string address2)
{
...
}
the thing is linq does'nt let me use my method (in a query passed in the "Query" method of the repository)
...
PersonRepository personRepository = new PersonRepository();
var person = repository.Query(p => AddressAreClose(adress,p.Adress);
...
therefor i needed to get All the elements of the table in a list using a simple foreach loop to make the tests and keeping only the relevant ones
...
PersonRepository personRepository = new PersonRepository();
var persons = personRepository.GetAll;
foreach(person in persons)
{
if(AdressAreClose(adress,person.adress))
...
}
for now i populated the database with only a few elements to test it, but i'm not sure it would work very well with the far more greater number it will contain later specially with all the test i'm planing to add
isn't there a more clever way to do this ??? I'm open to anything
Well first of all, you should use generics in your repository, even if it's constrained to Person. This way you can build pipes/filters off your queries to clean up your LINQ queries and facilitate reuse.
Of course, without seeing the full signature/implementation of your Query method, it's hard to tell. But either way, you need to return IEnumerable<Person> or IQueryable<Person> to make the following work.
So, you could turn AddressesAreClose into a pipe/filter, like this:
public static bool WhereAddressesAreClose(this IQueryable<Person> source, string address)
{
return source.Where(/* your conditions */);
}
Then you can use it in your LINQ query:
var person = repository
.Query() // Should be IQueryable<Person>
.WhereAddressAreClose(adress);
.ToList();
Depending on the size of your data and whether or not your implementing caching, you should limit the results on the server (database), not post-query with a foreach loop.
If the performance isn't great, consider adding indexes, using compiled queries or moving to a stored procedure.
I have an entity that I'd like to compare with a subset and determine to select all except the subset.
So, my query looks like this:
Products.Except(ProductsToRemove(), new ProductComparer())
The ProductsToRemove() method returns a List<Product> after it performs a few tasks. So in it's simplest form it's the above.
The ProductComparer() class looks like this:
public class ProductComparer : IEqualityComparer<Product>
{
public bool Equals(Product a, Product b)
{
if (ReferenceEquals(a, b)) return true;
if (ReferenceEquals(a, null) || ReferenceEquals(b, null))
return false;
return a.Id == b.Id;
}
public int GetHashCode(Product product)
{
if (ReferenceEquals(product, null)) return 0;
var hashProductId = product.Id.GetHashCode();
return hashProductId;
}
}
However, I continually receive the following exception:
LINQ to Entities does not recognize
the method
'System.Linq.IQueryable1[UnitedOne.Data.Sql.Product]
Except[Product](System.Linq.IQueryable1[UnitedOne.Data.Sql.Product],
System.Collections.Generic.IEnumerable1[UnitedOne.Data.Sql.Product],
System.Collections.Generic.IEqualityComparer1[UnitedOne.Data.Sql.Product])'
method, and this method cannot be
translated into a store expression.
Linq to Entities isn't actually executing your query, it is interpreting your code, converting it to TSQL, then executing that on the server.
Under the covers, it is coded with the knowledge of how operators and common functions operate and how those relate to TSQL. The problem is that the developers of L2E have no idea how exactly you are implementing IEqualityComparer. Therefore they cannot figure out that when you say Class A == Class B you mean (for example) "Where Person.FirstName == FirstName AND Person.LastName == LastName".
So, when the L2E interpreter hits a method it doesn't recognize, it throws this exception.
There are two ways you can work around this. First, develop a Where() that satisfies your equality requirements but that doesn't rely on any custom method. In other words, test for equality of properties of the instance rather than an Equals method defined on the class.
Second, you can trigger the execution of the query and then do your comparisons in memory. For instance:
var notThisItem = new Item{Id = "HurrDurr"};
var items = Db.Items.ToArray(); // Sql query executed here
var except = items.Except(notThisItem); // performed in memory
Obviously this will bring much more data across the wire and be more memory intensive. The first option is usually the best.
You're trying to convert the Except call with your custom IEqualityComparer into Entity SQL.
Obviously, your class cannot be converted into SQL.
You need to write Products.AsEnumerable().Except(ProductsToRemove(), new ProductComparer()) to force it to execute on the client. Note that this will download all of the products from the server.
By the way, your ProductComparer class should be a singleton, like this:
public class ProductComparer : IEqualityComparer<Product> {
private ProductComparer() { }
public static ProductComparer Instance = new ProductComparer();
...
}
The IEqualityComparer<T> can only be executed locally, it can't be translated to a SQL command, hence the error