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Jul 17, 2018
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Obsolete MultiQuery and MultiCriteria #1783

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8cc516b
Obsolete MultiQuery and MultiCriteria
fredericDelaporte Jul 4, 2018
7e40130
fixup! Obsolete MultiQuery and MultiCriteria
fredericDelaporte Jul 14, 2018
e8d4c5c
Merge branch 'master' into ObsoleteMultiQuery
fredericDelaporte Jul 14, 2018
9f7d805
fixup! Obsolete MultiQuery and MultiCriteria
fredericDelaporte Jul 14, 2018
b628962
fixup! Obsolete MultiQuery and MultiCriteria
fredericDelaporte Jul 16, 2018
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233 changes: 148 additions & 85 deletions doc/reference/modules/performance.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -1216,131 +1216,194 @@ sessionFactory.EvictCollection("Eg.Cat.Kittens");]]></programlisting>
</sect1>

<sect1 id="performance-multi-query">
<title>Multi Query</title>
<title>Query batch</title>

<para>
This functionality allows you to execute several HQL queries in one round-trip
This functionality allows you to execute several queries in one round-trip
against the database server. A simple use case is executing a paged query while
also getting the total count of results, in a single round-trip. Here is a simple
also getting the total count of results, in a single round-trip. Here is an
example:
</para>

<programlisting><![CDATA[using NHibernate.Multi;

...

IQueryBatch queries = s.CreateQueryBatch()
.Add<Item>(
s.CreateQuery("from Item i where i.Id > ?")
.SetInt32(0, 50).SetFirstResult(10))
.Add<long>(
s.CreateQuery("select count(*) from Item i where i.Id > :id")
.SetInt32("id", 50));
IList<Item> items = queries.GetResult<Item>(0);
long count = queries.GetResult<long>(1).Single();]]></programlisting>

<para>
The results are got by index, ordered according to the order of queries
added to the query batch. Instead of relying on this ordering, a key can be
associated with each query for later retrieval:
</para>

<programlisting><![CDATA[using NHibernate.Multi;

...

var queries = s.CreateQueryBatch()
.Add("list", s.Query<Item>().Where(i => i.Id > 50))
.Add("count", s.Query<Item>().Where(i => i.Id > 50), q => q.Count());
var count = queries.GetResult<int>("count").Single();
var items = queries.GetResult<Item>("list");]]></programlisting>

<para>
The namespace <literal>NHibernate.Multi</literal> has to be imported since most query
batch methods are extension methods.
</para>

<para>
Criteria queries are also supported by the query batch:
</para>

<programlisting><![CDATA[IMultiQuery multiQuery = s.CreateMultiQuery()
.Add(s.CreateQuery("from Item i where i.Id > ?")
.SetInt32(0, 50).SetFirstResult(10))
.Add(s.CreateQuery("select count(*) from Item i where i.Id > ?")
.SetInt32(0, 50));
IList results = multiQuery.List();
IList items = (IList)results[0];
long count = (long)((IList)results[1])[0];]]></programlisting>
<programlisting><![CDATA[var queries = s.CreateQueryBatch()
.Add<Item>(
s.CreateCriteria(typeof(Item))
.Add(Expression.Gt("Id", 50))
.SetFirstResult(10))
.Add<long>(
s.CreateCriteria(typeof(Item))
.Add(Expression.Gt("Id", 50))
.SetProject(Projections.RowCount()));
var items = queries.GetResult<Item>(0);
var count = queries.GetResult<long>(1).Single();]]></programlisting>

<para>
The result is a list of query results, ordered according to the order of queries
added to the multi query. Named parameters can be set on the multi query, and are
shared among all the queries contained in the multi query, like this:
You can add <literal>ICriteria</literal> or <literal>DetachedCriteria</literal> to the query batch.
In fact, using DetachedCriteria in this fashion has some interesting implications.
</para>
<programlisting><![CDATA[DetachedCriteria customersCriteria = AuthorizationService.GetAssociatedCustomersQuery();
IQueryBatch queries = session.CreateQueryBatch()
.Add<Customer>(customersCriteria)
.Add<Policy>(DetachedCriteria.For<Policy>()
.Add(Subqueries.PropertyIn("id",
CriteriaTransformer.Clone(customersCriteria)
.SetProjection(Projections.Id())
)));

<programlisting><![CDATA[IList results = s.CreateMultiQuery()
.Add(s.CreateQuery("from Item i where i.Id > :id")
.SetFirstResult(10))
.Add("select count(*) from Item i where i.Id > :id")
.SetInt32("id", 50)
.List();
IList items = (IList)results[0];
long count = (long)((IList)results[1])[0];]]></programlisting>
IList<Customer> customers = queries.GetResult<Customer>(0);
IList<Policy> policies = queries.GetResult<Policy>(1);]]></programlisting>

<para>
Positional parameters are not supported on the multi query, only on the individual
queries.
We get a query that represents the customers we can access, and then we can utilize this
query further in order to perform additional logic (getting the policies of the customers we are
associated with), all in a single database round-trip.
</para>

<para>
As shown above, if you do not need to configure the query separately, you can simply
pass the HQL directly to the <literal>IMultiQuery.Add()</literal> method.
The query batch also supports QueryOver and sql queries. All kind of queries can be mixed in the
same batch.
</para>

<programlisting><![CDATA[using NHibernate.Multi;

...

var queries = s.CreateQueryBatch()
.Add("queryOverList", s.QueryOver<Item>().Where(i => i.Category == "Food"))
.Add<long>("sqlCount",
s.CreateSQLQuery("select count(*) as itemCount from Item i where i.Category = :cat")
.AddScalar("itemCount", NHibernateUtil.Int64)
.SetString("cat", "Food"));
var count = queries.GetResult<long>("sqlCount").Single();
var items = queries.GetResult<Item>("queryOverList");]]></programlisting>

<para>
Second level cache is supported by the query batch. Queries flagged as cacheable will be retrieved
from the cache if already cached, otherwise their results will be put in the cache.
</para>

<programlisting><![CDATA[using NHibernate.Multi;

...

var queries = s.CreateQueryBatch()
.Add("list",
s.Query<Item>()
.Where(i => i.Id > 50)
.WithOptions(o => o.SetCacheable(true)))
.Add<long>("count",
s.CreateQuery("select count(*) from Item i where i.Id > :id")
.SetInt32("id", 50)
.SetCacheable(true));
var count = queries.GetResult<long>("count").Single();
var items = queries.GetResult<Item>("list");]]></programlisting>

<para>
Multi query is executed by concatenating the queries and sending the query to the database
as a single string. This means that the database should support returning several result sets
in a single query. At the moment this functionality is only enabled for Microsoft SQL Server and SQLite.
in a single query. Otherwise each query will be individually executed instead.
</para>

<para>
The first <literal>GetResult</literal> call triggers execution of the whole query batch, which
then stores all results. Later calls only retrieve the stored results. A query batch can be
re-executed by calling its <literal>Execute</literal> method. Once executed, no new query can be
added to the batch.
</para>

<para>
Note that the database server is likely to impose a limit on the maximum number of parameters
in a query, in which case the limit applies to the multi query as a whole. Queries using
Note that the database server is likely to enforce a limit on the maximum number of parameters
in a query, in which case the limit applies to the query batch as a whole. Queries using
<literal>in</literal> with a large number of arguments passed as parameters may easily exceed
this limit. For example, SQL Server has a limit of 2,100 parameters per round-trip, and will
throw an exception executing this query:
</para>

<programlisting><![CDATA[IList allEmployeesId = ...; //1,500 items
IMultiQuery multiQuery = s.CreateMultiQuery()
.Add(s.CreateQuery("from Employee e where e.Id in :empIds")
.SetParameter("empIds", allEmployeesId).SetFirstResult(10))
.Add(s.CreateQuery("select count(*) from Employee e where e.Id in :empIds")
.SetParameter("empIds", allEmployeesId));
IList results = multiQuery.List(); // will throw an exception from SQL Server]]></programlisting>

<programlisting><![CDATA[int[] allEmployeesId = ...; // 1,500 items
var queries = s.CreateQueryBatch()
.Add<Employee>(
s.CreateQuery("from Employee e where e.Id in :empIds")
.SetParameterList("empIds", allEmployeesId)
.SetFirstResult(10))
.Add<long>(
s.CreateQuery("select count(*) from Employee e where e.Id in :empIds")
.SetParameterList("empIds", allEmployeesId));
queries.Execute(); // will throw an exception from SQL Server]]></programlisting>

<para>
An interesting usage of this feature is to load several collections of an object in one
An interesting usage of the query batch is to load several collections of an object in one
round-trip, without an expensive cartesian product (blog * users * posts).
</para>

<programlisting><![CDATA[Blog blog = s.CreateMultiQuery()
.Add("select b from Blog b left join fetch b.Users where b.Id = :id")
.Add("select b from Blog b left join fetch b.Posts where b.Id = :id")
.SetInt32("id", 123)
.UniqueResult<Blog>();]]></programlisting>
<programlisting><![CDATA[Blog blog = s.CreateQueryBatch()
.Add(
s.CreateQuery("select b from Blog b left join fetch b.Users where b.Id = :id")
.SetInt32("id", 123))
.Add(
s.CreateQuery("select b from Blog b left join fetch b.Posts where b.Id = :id")
.SetInt32("id", 123))
.GetResult<Blog>(0).FirstOrDefault();]]></programlisting>

</sect1>

<sect1 id="performance-multi-criteria">
<title>Multi Criteria</title>

<para>
This is the counter-part to Multi Query, and allows you to perform several criteria queries
in a single round trip. A simple use case is executing a paged query while
also getting the total count of results, in a single round-trip. Here is a simple
example:
You can also add queries as future queries to a query batch:

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</para>

<programlisting><![CDATA[IMultiCriteria multiCrit = s.CreateMultiCriteria()
.Add(s.CreateCriteria(typeof(Item))
.Add(Expression.Gt("Id", 50))
.SetFirstResult(10))
.Add(s.CreateCriteria(typeof(Item))
.Add(Expression.Gt("Id", 50))
.SetProject(Projections.RowCount()));
IList results = multiCrit.List();
IList items = (IList)results[0];
long count = (long)((IList)results[1])[0];]]></programlisting>

<para>
The result is a list of query results, ordered according to the order of queries
added to the multi criteria.
</para>
<programlisting><![CDATA[using NHibernate.Multi;

<para>
You can add <literal>ICriteria</literal> or <literal>DetachedCriteria</literal> to the Multi Criteria query.
In fact, using DetachedCriteria in this fashion has some interesting implications.
</para>
<programlisting><![CDATA[DetachedCriteria customersCriteria = AuthorizationService.GetAssociatedCustomersQuery();
IList results = session.CreateMultiCriteria()
.Add(customersCriteria)
.Add(DetachedCriteria.For<Policy>()
.Add(Subqueries.PropertyIn("id",
CriteriaTransformer.Clone(customersCriteria)
.SetProjection(Projections.Id())
)))
.List();
...

ICollection<Customer> customers = CollectionHelper.ToArray<Customer>(results[0]);
ICollection<Policy> policies = CollectionHelper.ToArray<Policy>(results[1]);]]></programlisting>
var queries = s.CreateQueryBatch();
var list = queries.AddAsFuture(s.Query<Item>().Where(i => i.Id > 50)));
var countValue = queries.AddAsFutureValue<long>(
s.CreateQuery("select count(*) from Item i where i.Id > :id")
.SetInt32("id", 50));
var count = countValue.Value;
var items = list.GetEnumerable();]]></programlisting>

<para>
As you see, we get a query that represents the customers we can access, and then we can utilize this query further in order to
perform additional logic (getting the policies of the customers we are associated with), all in a single database round-trip.
Futures built from a query batch are executed together the first time the result of one of
them is accessed. They are independent of futures obtained directly from the queries.
</para>

</sect1>

<sect1 id="performance-future">
Expand Down
55 changes: 54 additions & 1 deletion src/NHibernate.Test/Async/Criteria/Lambda/IntegrationFixture.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
using NUnit.Framework;

using NHibernate.Criterion;
using NHibernate.Multi;

namespace NHibernate.Test.Criteria.Lambda
{
Expand Down Expand Up @@ -352,7 +353,7 @@ public async Task FunctionsOrderAsync()
}
}

[Test]
[Test, Obsolete]
public async Task MultiCriteriaAsync()
{
var driver = Sfi.ConnectionProvider.Driver;
Expand Down Expand Up @@ -408,6 +409,58 @@ public async Task MultiCriteriaAsync()
}
}

[Test]
public async Task MultiQueryAsync()
{
await (SetupPagingDataAsync());

using (var s = OpenSession())
{
var query =
s.QueryOver<Person>()
.JoinQueryOver(p => p.Children)
.OrderBy(c => c.Age).Desc
.Skip(2)
.Take(1);

var multiQuery =
s.CreateQueryBatch()
.Add("page", query)
.Add<int>("count", query.ToRowCountQuery());

var pageResults = await (multiQuery.GetResultAsync<Person>("page", CancellationToken.None));
var countResults = await (multiQuery.GetResultAsync<int>("count", CancellationToken.None));

Assert.That(pageResults.Count, Is.EqualTo(1));
Assert.That(pageResults[0].Name, Is.EqualTo("Name 3"));
Assert.That(countResults.Count, Is.EqualTo(1));
Assert.That(countResults[0], Is.EqualTo(4));
}

using (var s = OpenSession())
{
var query =
QueryOver.Of<Person>()
.JoinQueryOver(p => p.Children)
.OrderBy(c => c.Age).Desc
.Skip(2)
.Take(1);

var multiCriteria =
s.CreateQueryBatch()
.Add("page", query)
.Add<int>("count", query.ToRowCountQuery());

var pageResults = await (multiCriteria.GetResultAsync<Person>("page", CancellationToken.None));
var countResults = await (multiCriteria.GetResultAsync<int>("count", CancellationToken.None));

Assert.That(pageResults.Count, Is.EqualTo(1));
Assert.That(pageResults[0].Name, Is.EqualTo("Name 3"));
Assert.That(countResults.Count, Is.EqualTo(1));
Assert.That(countResults[0], Is.EqualTo(4));
}
}

private async Task SetupPagingDataAsync(CancellationToken cancellationToken = default(CancellationToken))
{
using (ISession s = OpenSession())
Expand Down
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