I have a hotel table, and an amenity table. The only way they are "related" is via location, using PostGIS for PostgreSQL. In SQL I use a query like this to find the 5 nearest amenities to a hotel:
SELECT amenity.name, amenity.brand, ST_Distance_Sphere(hotel.geom, amenity.geom)
FROM amenity, hotel
WHERE slug='city-plaza'
ORDER BY ST_Distance(hotel.geom, amenity.geom)
LIMIT 5;
Is there a way I could add a "nearestAmenities" field to the Hotel model using Bookshelf, which would be a collection of Amenity?
Have you tried using the knex.raw functionality?
knex.raw('SELECT amenity.name, amenity.brand, ... LIMIT 5').then(function(resp) {
...
});
The solution I found to this was to use SQL views in addition to Bookshelf's belongsToMany feature. Here are the steps using the above table names, in case anyone else stumbles upon this question:
1) Add a view 'hotel_amenity':
CREATE OR REPLACE VIEW hotel_amenity AS
SELECT h.id hotel_id,
a.id amenity_id,
ceil(ST_Distance(ST_Transform(h.geom, 3414), ST_Transform(a.geom, 3414))/100)/10 distance_km
FROM amenity a
CROSS JOIN hotel h;
2) Add a Amenity model with Bookshelf:
var Amenity = exports.Amenity = Bookshelf.Model.extend({
tableName: 'amenity'
});
3) Add a Hotel model with Bookshelf, and reference Amenity using belongsToMany:
var Hotel = exports.Hotel = Bookshelf.Model.extend({
tableName: 'hotel',
nearbyAmenities: function() {
return this.belongsToMany(Amenity, 'hotel_amenity')
.withPivot('distance_km')
.query('orderBy', 'distance_km', 'asc')
.query('limit', 10);
}
});
And don't forget to use withRelated when you fetch Hotel.
Related
I am comming to ASP .NET Core from PHP w/ MySQL.
The problem:
For the illustration, suppose the following two tables:
T: {ID, Description, FK} and States: {ID, ID_T, Time, State}. There is 1:n relationship between them (ID_T references T.ID).
I need all the records from T with some specific value of FK (lets say 1) along with the related newest record in States (if any).
In terms of SQL it can be written as:
SELECT T.ID, T.Description, COALESCE(s.State, 0) AS 'State' FROM T
LEFT JOIN (
SELECT ID_T, MAX(Time) AS 'Time'
FROM States
GROUP BY ID_T
) AS sub ON T.ID = sub.ID_T
LEFT JOIN States AS s ON T.ID = s.ID_T AND sub.Time = s.Time
WHERE FK = 1
I am struggling to write an efficient equivalent query in LINQ (or the fluent API). The best working solution I've got so far is:
from t in _context.T
where t.FK == 1
join s in _context.States on t.ID equals o.ID_T into _s
from s in _s.DefaultIfEmpty()
let x = new
{
id = t.ID,
time = s == null ? null : (DateTime?)s.Time,
state = s == null ? false : s.State
}
group x by x.id into x
select x.OrderByDescending(g => g.time).First();
When I check the resulting SQL query in the output window when executed it is just like:
SELECT [t].[ID], [t].[Description], [t].[FK], [s].[ID], [s].[ID_T], [s].[Time], [s].[State]
FROM [T] AS [t]
LEFT JOIN [States] AS [s] ON [T].[ID] = [s].[ID_T]
WHERE [t].[FK] = 1
ORDER BY [t].[ID]
Not only it selects more columns than I need (in the real scheme there are more of them). There is no grouping in the query so I suppose it selects everything from the DB (and States is going to be huge) and the grouping/filtering is happening outside the DB.
The questions:
What would you do?
Is there an efficient query in LINQ / Fluent API?
If not, what workarounds can be used?
Raw SQL ruins the concept of abstracting from a specific DB technology and its use is very clunky in current Entity Framework Core (but maybe its the best solution).
To me, this looks like a good example for using a database view - again, not really supported by Entity Framework Core (but maybe its the best solution).
What happens if you try to do a more straight forward translation to LINQ?
var latestState = from s in _context.States
group s by s.ID_T into sg
select new { ID_T = sg.Key, Time = sg.Time.Max() };
var ans = from t in _context.T
where t.FK == 1
join sub in latestState on t.ID equals sub.ID_T into subj
from sub in subj.DefaultIfEmpty()
join s in _context.States on new { t.ID, sub.Time } equals new { s.ID, s.Time } into sj
from s in sj.DefaultIfEmpty()
select new { t.ID, t.Description, State = (s == null ? 0 : s.State) };
Apparently the ?? operator will translate to COALESCE and may handle an empty table properly, so you could replace the select with:
select new { t.ID, t.Description, State = s.State ?? 0 };
OK. Reading this article (almost a year old now), Smit's comment to the original question and other sources, it seems that EF Core is not really production ready yet. It is not able to translate grouping to SQL and therefore it is performed on the client side, which may be (and in my case would be) a serious problem. It corresponds to the observed behavior (the generated SQL query does no grouping and selects everything in all groups). Trying the LINQ queries out in Linqpad it always translates to a single SQL query.
I have downgraded to EF6 following this article. It required some changes in my model's code and some queries. After changing .First() to .FirstOrDefault() in my original LINQ query it works fine and translates to a single SQL query selecting only the needed columns. The generated query is much more complex than it is needed, though.
Using a query from NetMage's answer (after small fixes), it results in a SQL query almost identical to my own original SQL query (there's only a more complex construct than COALESCE).
var latestState = from s in _context.States
group s by s.ID_T into sg
select new { ID = sg.Key, Time = sg.Time.Max() };
var ans = from t in _context.T
where t.FK == 1
join sub in latestState on t.ID equals sub.ID into subj
from sub in subj.DefaultIfEmpty()
join s in _context.States
on new { ID_T = t.ID, sub.Time } equals new { s.ID_T, s.Time }
into sj
from s in sj.DefaultIfEmpty()
select new { t.ID, t.Description, State = (s == null ? false : s.State) };
In LINQ it's not as elegant as my original SQL query but semantically it's the same and it does more or less the same thing on the DB side.
In EF6 it is also much more convenient to use arbitrary raw SQL queries and AFAIK also the database views.
The biggest downside of this approach is that full .NET framework has to be targeted, EF6 is not compatible with .NET Core.
I got about 5 look-a-like linq querys just like this SortPerson() metod. I'm trying to develop a search using dropdowns where a user can select values from the dropdown and returns the values that are true from one or more dropdowns the user has selected to use.
Is there a simpler way to develop this? help would be much appreciated
public void SortPerson()
{
var personId = ddlPerson.SelectedValue;
var data = new MyModelContext();
var documents = from d in data.tblDocuments
join sp in data.tblPersons on d.DocPerson equals sp.PersonId
select d;
if (!String.IsNullOrEmpty(personId))
{
documents = documents.Where(c => c.DocPerson.Equals(personId));
}
rptResult.DataSource = documents.ToList();
rptResult.DataBind();
}
I don't see the point in joining without Where if you still select only one table.
If you want all document in case when Person is not selected, then you can't create much simpler method. You can write it shorter like:
var documents =
from d in data.tblDocuments
join ...
where String.IsNullOrEmpty(personId) || d.DocPerson equals personId
select d;
so you don't need separate if statement.
If you want to use several values from 5 dropdowns and use them as conditions in single query, just add more conditions:
var personId = ddlPerson.SelectedValue;
var someValue = ddlSomeDDL.SelectedValue;
//3 more values from DDL
var documents = from d in data.tblDocuments
join sp in data.tblPersons on d.DocPerson equals sp.PersonId
where (String.IsNullOrEmpty(personId) || sp.PersonId equals personId)
&& (String.IsNullOrEmpty(someValue) || d.SomeColumn equals someValue)
//3 more conditions
select d;
I'm trying to use JoinSqlBuilder to select a data from one of the joined tables, and can't find a way to do that unless I list all columns from that table. Hopefully I'm missing something and it actually can be done.
This is approximately what I have:
var sql = new JoinSqlBuilder<Product, Product>()
.Join<Product, Customer>(src => src.Id, dst => dst.Id)
.Where<Customer>(x => x.Id == Id);
and I want to select everything from a product table. The query above throws an exception complaining about column name collisions, so its clearly does a select from both tables.
Edit: In the end I want to have this sql (never mind the design, its not a real thing):
select
p.* //<-- This is the piece that I'm struggling with
from product p inner join customer c on p.id on c.productId
where blah;
Looks like OrmLite want me to explicitly list all columns I want to return, which I want to avoid.
Note: I'm using 3.9.71 of servicestack. I've not looked at the 4.0 implementation yet.
I think you have a FK relationship problem with your join. Assuming that a product has a customer FK named (CustID), it'd look like this. Additionally, you'd need a POCO to represent the result set, if you are returning a "combination" of the results. I don't think you'll want to return both "ID" columns, and instead return a FK column.
return _factory.Run<ProductCustomer>(conn=>
{
var jn = new JoinSqlBuilder<Product, Customer>();
jn = jn.Join<Product, Customer>(srcProd => srcProd.CustId,
dstCust => dstCust.Id, // set up join Customer.id -> Product.CustId
p => new { p.Id, p.OtherField}, // product table fields returned
c => new { c.Name, c.AddressId}, // customer fields returned
null, //where clause on the product table
cust=>cust.Id = customerId // where clause on the customer table
);
var sql = jn.ToSQL();
return conn.FirstOrDefault<ProductCustomer>(sql);
}
Hope this helps.
Edit: After your Edit, try this:
// set up join Customer.id -> c.ProductId
jn = jn.Join<Product, Customer>(srcProd => srcProd.Id, dstCust => dstCust.productId)
.Where<Customer>(c=>c.Id == custIdParameter);
var sql = jn.ToSql();
You can add a ".Where" again for the
Where<Product>(p=>p.id == foo);
if you need to add more product with your BLAH. This should get you close.
Have you tried the SelectAll extension method?
var sql = new JoinSqlBuilder<Product, Product>()
.Join<Product, Customer>(src => src.Id, dst => dst.Id)
.SelectAll<Product>()
.Where<Customer>(x => x.Id == Id);
I have three tables: Schools (id, school_name), Schools_Focuses (id, school_id, focus_id) and Focuses (id, focus) and want to create a method on my Schools model that returns all related Focuses.
I can perform what I want to do with this SQL QUERY:
SELECT focus FROM focuses INNER JOIN schools_focuses ON focuses.id = schools_focuses.focus_id INNER JOIN schools ON schools.id = schools_focuses.school_id WHERE schools.id = 36;
Model code:
// Define Models
exports.School = School = Bookshelf.PG.Model.extend({
tableName: 'schools',
focuses: function() {
return this.hasMany(Focus).through(Schools_Focuses);
}
});
Error:
Possibly unhandled Error: column focuses.schools_focuse_id does not exist, sql: select "focuses".*, "schools_focuses"."id" as "_pivot_id", "schools_focuses"."school_id" as "_pivot_school_id" from "focuses" inner join "schools_focuses" on "schools_focuses"."id" = "focuses"."schools_focuse_id" where "schools_focuses"."school_id" in (?)
I don't want to have this extra column (focuses.schools_focuse_id) in Focuses because a focus can belongTo more than one school.
How can I correctly set this up? I have played around with the foreign keys and other keys for hasMany() and through() but no luck.
Thanks!
Sounds like you need to use belongsToMany() instead of hasMany().
// Define Models
exports.School = School = Bookshelf.PG.Model.extend({
tableName: 'schools',
focuses: function() {
return this.belongsToMany(Focus, 'schools_focuses');
}
});
The second parameter is needed since the join table isn't in alpha order ('focuses_schools'). And if it has problems identifying the join keys (school_id, focus_id) you can override those as parameters as well. Also, since it uses the join table internally, you don't need to create a separate model for Schools_Focuses.
If we don't need to create a separate model for Schools_Focuses, then how do we query data from the junction table i.e:
'SELECT * FROM focuses_schools WHERE focus_id = 2 & school_id = 1'
I have been trying to solve this problem and I can't seem to figure it out. I'm not sure if it's because of my db design and LINQ, but I'm hoping for some direction here.
My db table:
Id Name ParentId
1 Data1 null
2 Data2 null
3 Data3 null
4 Data4 1
5 Data5 1
6 Data6 2
7 Data7 2
Basically Data1 and Data2 are the top levels that I want to use for headings and their children will be related based on their ParentID.
I am trying to use a listview to present the data like the following:
Data1
-----
Data4
Data5
Data2
-----
Data6
Data7
I am trying to use a combination of LINQ and listview to accomplish this.
The following is the code for the linq query:
var query = from data in mydb.datatable
where data.ParentId == null
select data;
But this only gives the heading level... and unfortunately listview only takes in 1 datasource.
While it's possible with some databases (like SQL Server post 2005) to write recursive queries, I don't believe those get generated by LINQ. On the other hand, if the number of records is sufficiently small, you could materialize the data (to a list) and write a LINQ query that uses a recursive function to generate your list.
This is from memory, but it would look something like this:
Func<int?,IEnumerable<data>> f = null;
f = parentId => {
IEnumerable<data> result = from data in mydb.datatable
where data.ParentId = parentId
select data;
return result.ToList().SelectMany(d=>f(d.Id));
};
That should get you the hierarchy.
If your hierarchy has only two levels you can use a group join and anonymous objects:
var query = from data in mydb.datatable.Where(x => x.ParentId == null)
join child in mydb.datatable.Where(x => x.ParentId != null)
on data.Id equals child.ParentId into children
select new { data, children };
Edit: You will have to convert the data to a collection that can be bound to a ListView. One hack would be to have a list that is only one level deep with spacing in front of the subitems:
var listViewItems = (from item in query.AsEnumerable()
let dataName = item.data.Name
let childNames = item.children.Select(c => " " + c.Name)
from name in dataName.Concat(childNames)
select new ListViewItem(name)).ToArray();
You could also try to find a control that fits better, like a TreeView. You might want to ask a separate question about this issue.
I just wrote up a blog post describing a solution to build a graph from a self-referencing table with a single LINQ query to the database which might be of use. See http://www.thinqlinq.com/Post.aspx/Title/Hierarchical-Trees-from-Flat-Tables-using-LINQ.