I am using Entity Framework and Linq to SQL to select data from a database table. In my result object I am getting the tables being referenced by the selected table. Is there any way to restrict the referenced tables and get only the selected table. Below is my code.
var routeMaster = (from Ec_RouteMaster in travelServicesDBEntities.ExtraComfort_RouteMaster where (Ec_RouteMaster.Source == flights.OriginCode && Ec_RouteMaster.Destination == flights.DestinationCode && Ec_RouteMaster.AirCraftType == flights.AircraftType && Ec_RouteMaster.Switch == "1") select Ec_RouteMaster).FirstOrDefault();
I want data only from ExtraComfort_RouteMaster. But EF fetched data also from the tables referenced by the primary key of ExtraComfort_RouteMaster. How to do it?
Have a look at this and check the sections about lazy loading.
Related
I have an Object that maps column names to values. The columns to be updated are not known beforehand and are decided at run-time.
e.g. map = {col1: "value1", col2: "value2"}.
I want to execute an UPDATE query, updating a table with those columns to the corresponding values. Can I do the following? If not, is there an elegant way of doing it without building the query manually?
db.none('UPDATE mytable SET $1 WHERE id = 99', map)
is there an elegant way of doing it without building the query manually?
Yes, there is, by using the helpers for SQL generation.
You can pre-declare a static object like this:
const cs = new pgp.helpers.ColumnSet(['col1', 'col2'], {table: 'mytable'});
And then use it like this, via helpers.update:
const sql = pgp.helpers.update(data, cs) + /* WHERE clause with the condition */;
// and then execute it:
db.none(sql).then(data => {}).catch(error => {})
This approach will work with both a single object and an array of objects, and you will just append the update condition accordingly.
See also: PostgreSQL multi-row updates in Node.js
What if the column names are not known beforehand?
For that see: Dynamic named parameters in pg-promise, and note that a proper answer would depend on how you intend to cast types of such columns.
Something like this :
map = {col1: "value1", col2: "value2",id:"existingId"}.
db.none("UPDATE mytable SET col1=${col1}, col2=${col2} where id=${id}", map)
I'm trying to figure out how to replicate the below query in SQLAlchemy
SELECT c.company_id AS company_id,
(SELECT policy_id FROM associative_table at WHERE at.company_id = c.company_id) AS policy_id_ref,
(SELECT `default` FROM policy p WHERE p.policy_id = policy_id_ref) AS `default`,
FROM company c;
Note that this is a stripped down, basic example of what I'm really dealing with. The actual schema supports data and relationship versioning that requires the subqueries to include additional conditions, sorting, and limiting, making it impractical (if not impossible) for them to be joins.
The crux of the problem is in how the second subquery relies on policy_id_ref -- the value obtained from the first subquery. In SQLAlchemy, this is effectively what I have now:
ct = aliased(classes.company)
at = aliased(classes.associative_table)
pt = aliased(classes.policy)
policy_id_ref = session.query(at.policy_id).\
filter(at.company_id == ct.company_id).\
label('policy_id_ref')
policy_default = session.query(pt.default).\
filter(pt.id == 'policy_id_ref').\
label('default')
query = session.query(ct.company_id,policy_id_ref,policy_default)
The pull from the "company" table works fine as does the first subquery that retrieves the "policy_id_ref" column. The problem is the second subquery that has to reference that "policy_id_ref" column. I don't know how to write its filter in such a way that it literally renders "policy_id_ref" in the resulting query, to match the label of the first subquery.
Suggestions?
Thanks in advance
You can write your query as
select(
Companies.company_id,
AssociativeTable.policy_id.label('policy_id_ref'),
Policy.default.label('policy_default'),
).select_from(
Companies,
).join(
AssociativeTable,
AssociativeTable.company_id == Companies.company_id,
).join(
Policy,
AssociativeTable.policy_id == Policy.id
)
but in case you need reference to label from subquery => use literal_column
from sqlalchemy import func, select, literal_column
session.query(
func.array_agg(
literal_column('batch_info'),
JSONB
).label('history')
).select_from(
select(
func.jsonb_build_object(
'batch_id', AccountingQueueBatch.id,
'batch_label', AccountingQueueBatch.label,
).label('batch_info')
).select_from(
AccountingQueueBatch,
)
)
How can I get a list of table names and definitions by either SQL statement or code behind for the Starcounter DB?
Metadata about created tables, their columns and indexes are stored in meta-data tables. Database classes are publicly exposed for corresponding meta-data tables.
Tables or types are described by Starcounter.Metadata.RawView and Starcounter.Metadata.ClrClass and both extends Starctouner.Metadata.Table. ClrClass contains description for loaded CLR classes only, while RawView describes all created tables. They include descriptions of user-defined classes/tables and metadata classes/tables.
For example, all loaded user-defined classes can be enumerated:
foreach(ClrClass c in Db.SQL<ClrClass>(
"select c from Starcounter.Metadata.ClrClass c where Updatable = ?", true)) {
Console.WriteLine(c.FullName);
}
Property Updatable of Table is true for user-defined tables and false for meta-data/system tables.
Properties or columns are described by Starcounter.Metadata.Member and its children. An example of enumerating all columns for all user-defined tables is:
foreach(Member m in Db.SQL<Member>(
"select m from Column m, RawView v where m.Table = v and v.Updatable = ?",
true)) {
Console.WriteLine(m.Name);
}
Indexes are described by Starcounter.Metadata.Index and Starcounter.Metadata.IndexedColumn.
Currently it is one-to-one match between database classes and tables. However, this and metadata schema might change in future.
I have downloaded Microsoft Dynamic Query API. And using the dynamic query to filter the data using dates. I have written following query :-
Entities db = new Entities();
DateTime d = new DateTime(2014, 1, 17);
var lst = db.MSTPriorityS.Where("ModifiedOn == #0", d.Date.ToString()).ToList();
The result count, i am getting is 0. While there is data in the database table.
Please advise what i am doing wrong?
i think the problem is where you cast DateTime to String probably,
you can create your query step by step, and type safe, follow 'Creating dynamic queries with entity framework'
you can use lambda expression instead: var lst = db.MSTPriorityS.Where(u => u.ModifiedOn == System.Data.Objects.EntityFunctions.TruncateTime(d))
I've a problem with LINQ. Basically a third party database that I need to connect to is using the now depreciated text field (I can't change this) and I need to execute a distinct clause in my linq on results that contain this field.
I don't want to do a ToList() before executing the Distinct() as that will result in thousands of records coming back from the database that I don't require and will annoy the client as they get charged for bandwidth usage. I only need the first 15 distinct records.
Anyway query is below:
var query = (from s in db.tSearches
join sc in db.tSearchIndexes on s.GUID equals sc.CPSGUID
join a in db.tAttributes on sc.AttributeGUID equals a.GUID
where s.Notes != null && a.Attribute == "Featured"
select new FeaturedVacancy
{
Id = s.GUID,
DateOpened = s.DateOpened,
Notes = s.Notes
});
return query.Distinct().OrderByDescending(x => x.DateOpened);
I know I can do a subquery to do the same thing as above (tSearches contains unique records) but I'd rather a more straightfoward solution if available as I need to change a number of similar queries throughout the code to get this working.
No answers on how to do this so I went with my first suggestion and retrieved the unique records first from tSearch then constructed a subquery with the non unique records and filtered the search results by this subquery. Answer below:
var query = (from s in db.tSearches
where s.DateClosed == null && s.ConfidentialNotes != null
orderby s.DateOpened descending
select new FeaturedVacancy
{
Id = s.GUID,
Notes = s.ConfidentialNotes
});
/* Now filter by our 'Featured' attribute */
var subQuery = from sc in db.tSearchIndexes
join a in db.tAttributes on sc.AttributeGUID equals a.GUID
where a.Attribute == "Featured"
select sc.CPSGUID;
query = query.Where(x => subQuery.Contains(x.Id));
return query;