问题
I\'ve found very similar questions here but none that match exactly what I\'m looking for. The two closest threads I\'ve found are (yes, they are different threads):
NHibernate many-to-many criteria (1)
NHibernate many-to-many criteria (2)
However, I think both of those are using direct Many-to-Many relationships. I am actually simulating the Many-to-Many relationship by having two One-to-Many relationships with a junction table, which is pretty standard practice. Here are my NHibernate mappings:
Files:
<class name=\"Files\" table=\"files\">
<id name=\"id\">
<generator class=\"identity\" />
</id>
<property name=\"name\" />
<bag name=\"files_attrs\" table=\"files_attrs\" lazy=\"true\">
<key column=\"file_id\" />
<one-to-many class=\"Files_Attrs\" />
</bag>
</class>
Attributes:
<class name=\"Attrs\" table=\"attrs\">
<id name=\"id\">
<generator class=\"identity\" />
</id>
<property name=\"name\" />
<property name=\"value\" />
<bag name=\"files_attrs\" table=\"files_attrs\" lazy=\"true\">
<key column=\"attr_id\" />
<one-to-many class=\"Files_Attrs\" />
</bag>
</class>
Joiner:
<class name=\"Files_Attrs\" table=\"files_attrs\">
<id name =\"id\">
<generator class=\"identity\" />
</id>
<many-to-one name=\"file\" cascade=\"all\" column=\"file_id\" />
<many-to-one name=\"attr\" cascade=\"all\" column=\"attr_id\" />
</class>
So my problem is exactly like the second link above, but done with a Junction Table. So:
Given a set of Attribute IDs, I\'m hoping to run a query that gives me the files that have ALL of those matching Attributes. I can easily run \"n\" queries for each Attribute ID in the set and compare each list for File IDs that appear in every list, but I feel like there should be an easier way to do this all at once with one query.
Example:
File | Attributes
----------+-----------------------------------------------------
foo.txt | (mode = read-only, view = visible)
bar.txt | (mode = read-write, security = all, view = visible)
duck.txt | (mode = read-only, view = hidden)
goose.txt | (more = read-only, security = owner, view = visible)
Given these attributes: mode = read-only and view = visible, I want to be returned only foo.txt and goose.txt.
Can anyone help me with this? Thanks.
回答1:
One way how to achieve this, could be to create as many subqueries joined by AND, as many attributes must be found/related to searched files
I searching for name / value
The first solution works with the name/value pairs, from upper layer. I.e user selected mode to be read-only... (the second will be a bit easier, expecting that we already have ID's of the searched Atttributes)
// Below I am using C# properties, which I guess are correct
// based on the mapping. Naming convention is more Java (camel)
// but this should work with above mapping
// (also - class name Contact, not File)
Files file = null; // this is an alias used below
// here the attributes collection represents search filter
// ... settings for which is user looking for
var attributes = new List<Attrs>
{
new Attrs{ name = "mode", value = "read-only" },
new Attrs{ name = "view", value = "visible" }
};
// Let's start with definition of the outer/top query
// which will return all files, which do meet all filter requirements
var query = session.QueryOver<Files>(() => file);
In the next step, we will iterate through attributes, i.e. filters collection
// here we will take each attribute and create a subquery
// all these subqueries, will be joined with AND
// so only these files, which do have all attributes, will be selected
foreach (var attr in attributes)
{
// create the subquery, returning the FileId
Attrs attribute = null;
var subQueryForAttribute = QueryOver.Of<Files_Attrs>()
.JoinQueryOver(fa => fa.attr, () => attribute)
.Select(x => x.file.id)
;
// now, take name and value
var name = attr.name;
var value = attr.value;
// and convert them into where condition
subQueryForAttribute.Where(() => attribute.name == name);
subQueryForAttribute.Where(() => attribute.value == value);
// finally, add this subquery as a restriction to the top level query
query.WithSubquery
.WhereProperty(() => file.id)
.In(subQueryForAttribute);
}
Now we have a query, which is ready to support paging - because we are working on a flat structure of files. So we can use Take and skip if needed and then get the list of searched files
// query.Take(25);
// query.Skip(100);
var list = query.List<Files>();
This is a query which will result in a SELECT like this
SELECT ...
FROM files
WHERE id IN (SELECT file_Id FROM files_attrs
INNER JOIN attrs ON attrs.id = file_attrs.attr_id
WHERE name = 'mode' AND value = 'read-only' )
AND id IN (SELECT file_Id FROM files_attrs
INNER JOIN attrs ON attrs.id = file_attrs.attr_id
WHERE name = 'view' AND value = 'visible' )
II searching by attributes ID
The second solution, has easier starting conditions, instead of attributes (name and value) we already have their Ids (cite from a question:)
Given a set of Attribute IDs, I'm hoping to run a query that gives me the files that have ALL of those matching Attributes.
// Below I am using C# properties, which I guess are correct
// based on the mapping. Naming convention is more Java (camel)
// but this should work with above mapping
// (also - class name Files, not File)
Files file = null; // this is an alias used below
// here the attributeIds collection represents attributes to be found
var attributeIds = new List<int> { 1, 4, 5 };
// Let's again start with definition of the outer/top query
// which will return all files, which do meet all filter requirements
var query = session.QueryOver<Files>(() => file);
Next is the iteration through the set of known IDs which must exist as relation (all of them)
// here we will take each attribute and create a subquery
// all these subqueries, will be joined with AND
// so only these files, which do have all attributes, will be selected
foreach (var attrId in attributeIds)
{
// create the subquery, returning the Files.id
var subQueryForAttribute = QueryOver.Of<Files_Attrs>()
// no need to join, all the stuff is in the pairing table
.Select(x => x.file.id)
;
var id = attrId; // local variable
// and convert them into where condition
subQueryForAttribute.Where(pair => pair.attr.id == id);
// finally, add this subquery as a restriction to the top level query
query.WithSubquery
.WhereProperty(() => file.id)
.In(subQueryForAttribute);
}
var list = query.List<Files>();
The solution with known IDS is a bit easier (less tables are needed in SQL statemenets)
NOTE: have to say: it is great to see, that you've introduced the many-to-one and one-to-many instead of many-to-many. I would, personally, say that exactly this example shows, how big profit it could bring... ability to search even with complex filters
Some links, to show the power of the QueryOver: Query on HasMany reference , and some good reason why not to use many-to-many mapping: many-to-many with extra columns nhibernate
回答2:
Im not sure if this is what you need:
<bag name="files_attrs" table="files_attrs" lazy="true" where="something like '%mode = read-only%' and something like '%view = visible%'">
<key column="attr_id" />
<one-to-many class="Files_Attrs" />
</bag>
Where something is the attribute or is the column where is the data to filter.
Try this query:
Files fAlias = null;
Attrs aAlias = null;
var disjunction = new Disjunction();
disjunction.Add(Restrictions.On(() => aAlias.value)
.IsLike("mode = read-only", MatchMode.Anywhere));
disjunction.Add(Restrictions.On(() => aAlias.value)
.IsLike("view = visible", MatchMode.Anywhere));
var subquery = QueryOver.Of<Files_Attrs>
.Inner.JoinAlias(x => x.file, () => fAlias)
.Inner.JoinAlias(x => x.attr, () => aAlias)
.Where(disjunction)
.Select(() => fAlias);
var files = session.QueryOver<Files>
.WithSubquery.WhereExists(subquery)
.List();
来源：https://stackoverflow.com/questions/23772548/nhibernate-many-to-many-query-using-junction-joiner-table