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Recursion in Fluent API

I am designing a fluent API for writing SQL. Keep in mind one of my goals is to have API not suggest functions that can't be called in that part of the chain. For instance if you just got done defining a field in the select clause you can't call Where until you called From first. A simple query looks like this:
string sql = SelectBuilder.Create()
.Select()
.Fld("field1")
.From("table1")
.Where()
.Whr("field1 > field2")
.Whr("CURRENT_TIMESTAMP > field3")
.Build()
.SQL;
My problem comes with recursion in SQL code. Say you wanted to have a field contain another SQL statement like below:
string sql = SelectBuilder.Create()
.Select()
.Fld("field1")
.SQLFld()
.Select
.Count("field6")
.From("other table")
.EndSQLFld()
.FLd("field2")
.From("table1")
.Where()
.Whr("field1 > field2")
.Whr("CURRENT_TIMESTAMP > field3")
.Build()
.SQL;
I am using method chaining to build my fluent API. It many ways it is a state machine strewn out across many classes which represent each state. To add this functionality I would need to copy essentially every state I already have and wrap them around the two SQLFld and EndSQLFld states. I would need yet another copy if you were one more level down and were embedding a SQL statement in to a field of the already embedded SQL statement. This goes on to infinity, so with an infinitely deep embedded SQL query I would need an infinite number of classes to represent the infinite states.
I thought about writing a SelectBuilder query that was taken to the point of the Build method and then embedding that SelectBuilder in to another SelectBuilder and that fixes my infinity problem, but it is not very elegant and that is the point of this API.
I could also throw out the idea that the API only offers functions when they are appropriate but I would really hate to do that. I feel like that helps you best discover how to use the API. In many fluent APIs it doesn't matter which order you call what, but I want the API to appear as close to the actual SQL statement as possible and enforce its syntax.
Anyone have any idea how to solve this issue?

Glad to see you are trying fluent interfaces, I think they are a very elegant and expressive.
The builder pattern is not the only implementation for fluent interfaces. Consider this design, and let us know what you think =)
This is an example and I leave to you the details of your final implementation.
Interface design example:
public class QueryDefinition
{
// The members doesn't need to be strings, can be whatever you use to handle the construction of the query.
private string select;
private string from;
private string where;
public QueryDefinition AddField(string select)
{
this.select = select;
return this;
}
public QueryDefinition From(string from)
{
this.from = from;
return this;
}
public QueryDefinition Where(string where)
{
this.where = where;
return this;
}
public QueryDefinition AddFieldWithSubQuery(Action<QueryDefinition> definitionAction)
{
var subQueryDefinition = new QueryDefinition();
definitionAction(subQueryDefinition);
// Add here any action needed to consider the sub query, which should be defined in the object subQueryDefinition.
return this;
}
Example usage:
static void Main(string[] args)
{
// 1 query deep
var def = new QueryDefinition();
def
.AddField("Field1")
.AddField("Filed2")
.AddFieldWithSubQuery(subquery =>
{
subquery
.AddField("InnerField1")
.AddField("InnerFiled2")
.From("InnerTable")
.Where("<InnerCondition>");
})
.From("Table")
.Where("<Condition>");
// 2 queries deep
var def2 = new QueryDefinition();
def2
.AddField("Field1")
.AddField("Filed2")
.AddFieldWithSubQuery(subquery =>
{
subquery
.AddField("InnerField1")
.AddField("InnerField2")
.AddFieldWithSubQuery(subsubquery =>
{
subsubquery
.AddField("InnerInnerField1")
.AddField("InnerInnerField2")
.From("InnerInnerTable")
.Where("<InnerInnerCondition>");
})
.From("InnerInnerTable")
.Where("<InnerCondition>");
})
.From("Table")
.Where("<Condition>");
}

You can't "have only applicable methods available" without either sub-APIs for the substructures or clear bracketing/ending of all inner structural levels (SELECT columns, expressions in WHERE clause, subqueries).
Even then, running it all through a single API will require it to be stateful & "modal" with "bracketing" methods, to track whereabouts in the decl you are. Error reporting & getting these right will be tedious.
Ending bracketing by "fluent" methods, to me, seems non-fluent & ugly. This would result in a ugly appearence of EndSelect, EndWhere, EndSubquery etc. I'd prefer to build substructures (eg SUBQUERY for select) into a local variable & add that.
I don't like the EndSQLFld() idiom, which terminates the Subquery implicitly by terminating the Field. I'd prefer & guess it would be better design to terminate the subquery itself which is the complex part of the nested structure -- not the field.
To be honest, trying to enforce ordering of a "declarative" API for a "declarative" language (SQL) seems to be a waste of time.
Probably what I'd consider closer to an ideal usage:
SelectBuilder select = SelectBuilder.Create("CUSTOMER")
.Column("ID")
.Column("NAME")
/*.From("CUSTOMER")*/ // look, I'm just going to promote this onto the constructor.
.Where("field1 > field2")
.Where("CURRENT_TIMESTAMP > field3");
SelectBuilder countSubquery = SelectBuilder.Create("ORDER")
.Formula("count(*)");
.Where("ORDER.FK_CUSTOMER = CUSTOMER.ID");
.Where("STATUS = 'A'");
select.Formula( countSubquery, "ORDER_COUNT");
string sql = SelectBuilder.SQL;
Apologies to the Hibernate Criteria API :)

How to create a dynamic 'contains or LIKE' Expression to be used with Linq against OData service

I'm try'n to create a dynamic query tool using System.Linq.Expressions.Expression (WPF/c#4.0)
It runs against an OData Service.
So far, all is working as long as I limit the conditions to build in options like Equal(..), GreaterThan(..) etc.
There seems to be no build in contains/Like condition so I tried building my own. There are a handful of articles already out there. One I tried is How to create a System.Linq.Expressions.Expression for Like?.
Now if I use the above solution, the resulting where expression is
whereCallExpression = {Convert([10000]).Expand("A,B").Where(clt => MyLike(clt.LastName, "te"))}'
which is nice, but wrong, since it does not translate into a valid Odata query.
If I use condition 'Equal', the result is
whereCallExpression = {Convert([10000]).Expand("A,B").Where(clt => (clt.LastName == "te"))}
which results in the OData query
results = {http://.../Clients()?$filter=LastName eq 'te'&$expand=A,B}
and is working as expected.
Am I doing something wrong with the implementation of the solution, or can it not be used with OData?
It should transfer to something like ...?$filter=substringof('te', LastName ) eq true
Any solution on how to fix this?
Regards
Andreas
PS, I implemented the solution extension in a static class, all I changed is the name of the called method from 'Like' to 'MyLike'
Also, since the code used to build the expressions is working with any of the build-in condition, I assume, for now that part is ok. I can post parts of it if needed

OData currently doesn't support the "like" operator at all. So no matter what you do on the client, the URL produced has not way of expressing that.
The substringof is supported and the client LINQ provider should generate it when you use string.Contains method in your filter (Where) expression.
To get the expression generated by a C# compiler you can do something like this:
IQueryable<string> source = new List<string>().AsQueryable();
IQueryable<string> result = from item in source where item.Contains("John") select item;
Console.WriteLine(result.Expression.ToString());
Basically any IQueryable has a property Expression which contains the expression tree for the query to run. Some LINQ providers might change the expression tree somewhat from the original one created by the compiler, but most should leave it close to the original.

Using Dynamic LINQ (or Generics) to query/filter Azure tables

So here's my dilemma. I'm trying to utilize Dynamic LINQ to parse a search filter for retrieving a set of records from an Azure table. Currently, I'm able to get all records by using a GenericEntity object defined as below:
public class GenericEntity
{
public string PartitionKey { get; set; }
public string RowKey { get; set; }
Dictionary<string, object> properties = new Dictionary<string, object>();
/* "Property" property and indexer property omitted here */
}
I'm able to get this completely populated by utilizing the ReadingEntity event of the TableServiceContext object (called OnReadingGenericEvent). The following code is what actually pulls all the records and hopefully filter (once I get it working).
public IEnumerable<T> GetTableRecords(string tableName, int numRecords, string filter)
{
ServiceContext.IgnoreMissingProperties = true;
ServiceContext.ReadingEntity -= LogType.GenericEntity.OnReadingGenericEntity;
ServiceContext.ReadingEntity += LogType.GenericEntity.OnReadingGenericEntity;
var result = ServiceContext.CreateQuery<GenericEntity>(tableName).Select(c => c);
if (!string.IsNullOrEmpty(filter))
{
result = result.Where(filter);
}
var query = result.Take(numRecords).AsTableServiceQuery<GenericEntity>();
IEnumerable<GenericEntity> res = query.Execute().ToList();
return res;
}
I have TableServiceEntity derived types for all the tables that I have defined, so I can get all properties/types using Reflection. The problem with using the GenericEntity class in the Dynamic LINQ Query for filtering is that the GenericEntity object does NOT have any of the properties that I'm trying to filter by, as they're really just dictionary entries (dynamic query errors out). I can parse out the filter for all the property names of that particular type and wrap
"Property[" + propName + "]"
around each property (found by using a type resolver function and reflection). However, that seems a little... overkill. I'm trying to find a more elegant solution, but since I actually have to provide a type in ServiceContext.CreateQuery<>, it makes it somewhat difficult.
So I guess my ultimate question is this: How can I use dynamic classes or generic types with this construct to be able to utilize dynamic queries for filtering? That way I can just take in the filter from a textbox (such as "item_ID > 1023000") and just have the TableServiceEntity types dynamically generated.
There ARE other ways around this that I can utilize, but I figured since I started using Dynamic LINQ, might as well try Dynamic Classes as well.
Edit: So I've got the dynamic class being generated by the initial select using some reflection, but I'm hitting a roadblock in mapping the types of GenericEntity.Properties into the various associated table record classes (TableServiceEntity derived classes) and their property types. The primary issue is still that I have to initially use a specific datatype to even create the query, so I'm using the GenericEntity type which only contains KV pairs. This is ultimately preventing me from filtering, as I'm not able to do comparison operators (>, <, =, etc.) with object types.
Here's the code I have now to do the mapping into the dynamic class:
var properties = newType./* omitted */.GetProperties(
System.Reflection.BindingFlags.Instance |
System.Reflection.BindingFlags.Public);
string newSelect = "new(" + properties.Aggregate("", (seed, reflected) => seed += string.Format(", Properties[\"{0}\"] as {0}", reflected.Name)).Substring(2) + ")";
var result = ServiceContext.CreateQuery<GenericEntity>(tableName).Select(newSelect);
Maybe I should just modify the properties.Aggregate method to prefix the "Properties[...]" section with the reflected.PropertyType? So the new select string will be made like:
string newSelect = "new(" + properties.Aggregate("", (seed, reflected) => seed += string.Format(", ({1})Properties[\"{0}\"] as {0}", reflected.Name, reflected.PropertyType)).Substring(2) + ")";
Edit 2: So now I've hit quite the roadblock. I can generate the anonymous types for all tables to pull all values I need, but LINQ craps out on my no matter what I do for the filter. I've stated the reason above (no comparison operators on objects), but the issue I've been battling with now is trying to specify a type parameter to the Dynamic LINQ extension method to accept the schema of the new object type. Not much luck there, either... I'll keep you all posted.

I've created a simple System.Refection.Emit based solution to create the class you need at runtime.
http://blog.kloud.com.au/2012/09/30/a-better-dynamic-tableserviceentity/

I have run into exactly the same problem (with almost the same code :-)). I have a suspicion that the ADO.NET classes underneath somehow do not cooperate with dynamic types but haven't found exactly where yet.

So I've found a way to do this, but it's not very pretty...
Since I can't really do what I want within the framework itself, I utilized a concept used within the AzureTableQuery project. I pretty much just have a large C# code string that gets compiled on the fly with the exact object I need. If you look at the code of the AzureTableQuery project, you'll see that a separate library is compiled on the fly for whatever table we have, that goes through and builds all the properties and stuff we need as we query the table. Not the most elegant or lightweight solution, but it works, nevertheless.
Seriously wish there was a better way to do this, but unfortunately it's not as easy as I had hoped. Hopefully someone will be able to learn from this experience and possibly find a better solution, but I have what I need already so I'm done working on it (for now).

Pulling the WHERE clause out of LINQ to SQL

I'm working with a client who wants to mix LINQ to SQL with their in-house DAL. Ultimately they want to be able to query their layer using typical LINQ syntax. The point where this gets tricky is that they build their queries dynamically. So ultimately what I want is to be able to take a LINQ query, pull it apart and be able to inspect the pieces to pull the correct objects out, but I don't really want to build a piece to translate the 'where' expression into SQL. Is this something I can just generate using Microsoft code? Or is there an easier way to do this?

(you mean just LINQ, not really LINQ-to-SQL)
Sure, you can do it - but it is massive amounts of work. Here's how; I recommend "don't". You could also look at the source code for DbLinq - see how they do it.
If you just want Where, it is a bit easier - but as soon as you start getting joins, groupings, etc - it will be very hard to do.
Here's just Where support on a custom LINQ implemention (not a fully queryable provider, but enough to get LINQ with Where working):
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;
namespace YourLibrary
{
public static class MyLinq
{
public static IEnumerable<T> Where<T>(
this IMyDal<T> dal,
Expression<Func<T, bool>> predicate)
{
BinaryExpression be = predicate.Body as BinaryExpression;
var me = be.Left as MemberExpression;
if(me == null) throw new InvalidOperationException("don't be silly");
if(me.Expression != predicate.Parameters[0]) throw new InvalidOperationException("direct properties only, please!");
string member = me.Member.Name;
object value;
switch (be.Right.NodeType)
{
case ExpressionType.Constant:
value = ((ConstantExpression)be.Right).Value;
break;
case ExpressionType.MemberAccess:
var constMemberAccess = ((MemberExpression)be.Right);
var capture = ((ConstantExpression)constMemberAccess.Expression).Value;
switch (constMemberAccess.Member.MemberType)
{
case MemberTypes.Field:
value = ((FieldInfo)constMemberAccess.Member).GetValue(capture);
break;
case MemberTypes.Property:
value = ((PropertyInfo)constMemberAccess.Member).GetValue(capture, null);
break;
default:
throw new InvalidOperationException("simple captures only, please");
}
break;
default:
throw new InvalidOperationException("more complexity");
}
return dal.Find(member, value);
}
}
public interface IMyDal<T>
{
IEnumerable<T> Find(string member, object value);
}
}
namespace MyCode
{
using YourLibrary;
static class Program
{
class Customer {
public string Name { get; set; }
public int Id { get; set; }
}
class CustomerDal : IMyDal<Customer>
{
public IEnumerable<Customer> Find(string member, object value)
{
Console.WriteLine("Your code here: " + member + " = " + value);
return new Customer[0];
}
}
static void Main()
{
var dal = new CustomerDal();
var qry = from cust in dal
where cust.Name == "abc"
select cust;
int id = int.Parse("123");
var qry2 = from cust in dal
where cust.Id == id // capture
select cust;
}
}
}

Technically if your DAL exposes IQueryable<T> instead of IEnumerable<T> you can also implement a IQueryProvider and do exactly what you describe. However, this is not for the faint of heart.
But if you expose the LINQ to SQL tables themselves in the DAL, they will do exactly this for you. There is a (big) risk though since you'll be handling the client code total control over how to express SQL queries, and the usual result is some complex query that joins everything and slaps pagination a top of it with less than spectacular run time performance.
I think you should consider carefully what is actually needed from the DAL and expose only that.

I just read an interesting article on Expression Trees, LINQ to SQL uses these to translate the query into SQL and send it over the wire.
Maybe that's something you could use?

Just some though. I know some language support building a string that can be execute in the code itself. I never tried it with .Net, but this is common in functional languages like LISP. Since .Net support lambdas, maybe this is possible.
Since F# is coming to .Net soon, maybe it will possible if it is not right now.
What I am trying to say is if you can do this then maybe you can build that string that will be use as the LINQ statement and then execute it. Since it is a string, it will be possible to analyse the string and get the information you want.

Try Dynamic Linq

To anyone else with the same question out there. Pulling out the where clause from LINQ-to-SQL isn’t quite as straightforward, as one would’ve hoped for. Additionally, doing that by itself is probably meaningless. There are a couple of options, depending on the requirements – either grab it from the generated string, but then it would contain parameter references and object property mappings that would also have to be resolved, so those would also have to be pulled out of the original provider somehow, otherwise this would be pointless. Another – would be to find a modular provider that can do that, as well as make member mappings easily accessible, but once again, without the rest of the query, I see little utility in doing that, because the where clause would reference table/column aliases from the select statement.
I had a similar task to write a full blown provider for a custom ORM/DAL a couple of years ago. While it qualifies as the most complex thing I’ve worked on, being an experience developer, I can say it’s not as bad, as some people claim once you wrap your head around the concepts that lie at the foundation of such a component. Some solutions that I’ve seen go the wrong way about it, add redundant functionality and have extra code addressing problems introduced by underlying logic. E.g. the “optimization” stage/module that attempts to re-factor bloated, nested SQL produced by the main parser. If the latter was designed in such a way that would output clean SQL from the start, then no clean-up phase would be needed. I’ve seen providers that create a new level of nesting for each where and join call. That’s a bad strategy. By breaking down a query into three/four main parts – select, from, where and orderby, which are built individually as the tree is being visited, this problem is avoided altogether. I’ve developed an object-to-data (aka LINQ-to-SQL) provided based on these principles for a custom ORM/DAL and it produces nice, clean SQL, with an excellent performance, as each statement is compiled to IL and cached.
For anyone that is looking to do something similar, please see my posts that include a sample project with a tutorial/barebones implementation that makes it easy to see how it works. Included is also the full solution:
How to write a LINQ to SQL provider in C# Part 1 - Introduction
How to write a LINQ to SQL provider in C# Part 2 - Expression Visitor
How to write a LINQ to SQL provider in C# Part 3 - Where Clause Visitor
How to write a LINQ to SQL provider in C# Part 4 - Compiling Expression Trees

LINQ to SQL Custom Property query on where clause

I am using LINQ to SQL classes, and have extended one (with a partial class) and added an extra property. I want to query on this property, so:
(from p in db.TableName where p.CustomProperty=="value" select p)
However this doesn't work. I get an error: The member 'TableName.CustomProperty' has no supported translation to SQL. At the moment I have no code in the 'set' section of my Custom Property as I'm unsure how.
So basically, Custom Property which can be queried on with LINQ to SQL, how?
As a follow up: this CustomProperty is NOT a column in the table. It is a separate value, but I need to both fetch it (easy enough) but also query on it!

As you can understand, there can't be any magic, so essentially there will be two queries: first one is a SQL query with database criteria and on its result there should be applied your custom criteria as a second query.
So the workaround you could use is to split two parts explicitly like this:
var dbFetch = (from p in db.TableName where p.RealProperty ==" value" select p).ToArray();
var result = from p in dbFetch where p.CustomProperty == "value" select p;
But of course you'll run into several limitations. For example if you fetching results page-by-page, the second criterion will break paging since it performs additional filtering.
HTH

It's called LINQ to SQL. Just to avoid misunderstandings.
About your problem: have you added that property using the designer? And have you re-created the database after that?
If you did it by hand, make sure you have a private storage field (like _CustomProperty), and your property (CustomProperty) is marked with the ColumnAttribute, e.g.
private string _CustomProperty;
[Column(Storage="_CustomProperty", CanBeNull=true)]
public string CustomProperty
{
get { return _CustomProperty; }
}
Hope this helps.

Aren't you missing an equality sign there? In C#, equality is expressed with double equal signs, as in "a == b", while single equal sign signifies assignment, as in "obj.SomeProp = 5;"

I have implemented a system where you can query manually added properties that represent enumerated wrappers around integer properties from database columns. So I know it's possible, and it looks like you might be wanting to do something similar. The way I did it was not easy, though, and unless you are building a framework that you want to use properly for many cases, you might be better off using the solution suggested by archimed7592. I don't have the code handy at the moment so I can't provide all the details, but briefly my solution works like this. I created a custom LINQ provider, replacing the LINQ-to-SQL provider. I did this by implementing a custom IQueryable interface that returned my LINQ provider instead of that provided by LINQ-to-SQL. Then, in the functions that take expression objects, I pre-processed the expression before returning the result. I replaced all comparisons between enum-type properties and enum values with comparisons between integer properties and integer values, then passed that expression to the normal LINQ-to-SQL implementation in order to return the result. Since expressions are read-only, I had to make a (recursive) function that re-built the entire expression with the customized parts replaced.