I'm moving my app over from Sqlite-Net to Azure Mobile Services and I'm adding offline sync capabilities.
I'm unsure how to execute arbitrary queries. This is what I have for Sqlite-Net:
var newestDate = await this.connection.ExecuteScalarAsync<DateTime> ("SELECT MAX(TimeStamp) FROM SupplyData");
How can I run this query against my IMobileServiceSyncTable instance?
There is a CreateQuery() method but it does not take any parameters.
Is there any reason you can't use LINQ?
// This query filters out completed TodoItems and items without a timestamp.
List<TodoItem> items = await todoTable
.Where(todoItem => todoItem.Complete == false)
.ToListAsync();
Reference: https://azure.microsoft.com/en-us/documentation/articles/app-service-mobile-dotnet-how-to-use-client-library/#filtering
The alternate to this is to call a custom API. In ASP.NET backends, this is just a WebAPI that uses the underlying Entity Framework stuff. See https://azure.microsoft.com/en-us/documentation/articles/app-service-mobile-dotnet-backend-how-to-use-server-sdk/#how-to-define-a-custom-api-controller For Node.js backends (or Easy Tables / Easy API), see the following sample code: https://github.com/Azure/azure-mobile-apps-node/tree/master/samples/custom-api-sql-stmt
Related
I have a console app to test EF Core with SQL Server Express edition. I have the following code in Program.cs
using EFCoreTutorials;
using EFCoreTutorials.Entities;
using Microsoft.EntityFrameworkCore;
using (var context = new SalesManagementContext())
{
var employees = context.Employees.ToList();
}
I wonder why context.Employees brings all data from my employees table without even asking for it with a query. If I have many tables in my database and my context class with a lot of data , are all these available from the context var at the beginning of program without even specifying which one of these I actuall want to use?
Thank you
Two (JSF + JPA + EclipseLink + MySQL) applications share the same database. One application runs a scheduled task where the other one creates tasks for schedules. The tasks created by the first application is collected by queries in the second one without any issue. The second application updates fields in the task, but the changes done by the second application is not refreshed when queried by JPQL.
I have added QueryHints.CACHE_USAGE as CacheUsage.DoNotCheckCache, still, the latest updates are not reflected in the query results.
The code is given below.
How can I get the latest updates done to the database from a JPQL query?
public List<T> findByJpql(String jpql, Map<String, Object> parameters, boolean withoutCache) {
TypedQuery<T> qry = getEntityManager().createQuery(jpql, entityClass);
Set s = parameters.entrySet();
Iterator it = s.iterator();
while (it.hasNext()) {
Map.Entry m = (Map.Entry) it.next();
String pPara = (String) m.getKey();
if (m.getValue() instanceof Date) {
Date pVal = (Date) m.getValue();
qry.setParameter(pPara, pVal, TemporalType.DATE);
} else {
Object pVal = (Object) m.getValue();
qry.setParameter(pPara, pVal);
}
}
if(withoutCache){
qry.setHint(QueryHints.CACHE_USAGE, CacheUsage.DoNotCheckCache);
}
return qry.getResultList();
}
The CacheUsage settings affect what EclipseLink can query using what is in memory, but not what happens after it goes to the database for results.
It seems you don't want to out right avoid the cache, but refresh it I assume so the latest changes can be visible. This is a very common situation when multiple apps and levels of caching are involved, so there are many different solutions you might want to look into such as manual invalidation or even if both apps are JPA based, cache coordination (so one app can send an invalidation even to the other). Or you can control this on specific queries with the "eclipselink.refresh" query hint, which will force the query to reload the data within the cached object with what is returned from the database. Please take care with it, as if used in a local EntityManager, any modified entities that would be returned by the query will also be refreshed and changes lost
References for caching:
https://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Caching
https://www.eclipse.org/eclipselink/documentation/2.6/concepts/cache010.htm
Make the Entity not to depend on cache by adding the following lines.
#Cache(
type=CacheType.NONE, // Cache nothing
expiry=0,
alwaysRefresh=true
)
I'm trying to query a spring-data couchbase repository using N1QL queries. I have two doubts:
I'm using #Query annotation to generate queries, my code looks like this:
#Query("#{#n1ql.selectEntity} WHERE $0 = $1 AND #{#n1ql.filter}")
public Page<GsJsonStore> matchJson(String term, String value, Pageable pageable);
//Query
Page<GsJsonStore> p = repo.matchJson("_object.details.status", "ready", pg);
This query doesn't return any results. However, when I run the same query (below) in cbq I get the desired result:
select * from default where _object.details.status = 'ready';
How can I view the query string generated by the Couchbase repository? I'm using spring-boot. Am I correct in using the #Query annotation for this use-case?
Also, how can I perform n1QL queries on CouchbaseOperations template? I know that there's a findByN1QL method, but I didn't find any good documentation about it. Could someone please explain how to use this?
The query looks ok. You did persist your GsJsonStore entities using the Spring Data Couchbase repository did you?
In order to log all the queries generated and executed by the framework (including inline queries like in your case), you can configure the logger like so in a logback.xml configuration:
<logger name="org.springframework.data.couchbase.repository.query" level="debug"/>
You'll see that the query that got executed and the query that you ran in cbq are not the same, since at least you didn't use a WHERE clause.
In CouchbaseOperations there are two methods relative to N1QL queries:
findByN1QL: this expects specific structure of the query, in order to make sure all data necessary to correct deserialization of a Spring Data annotated entity is selected (which is the purpose of the #n1ql.selectEntity and #n1ql.filter SpEL).
findByN1QLProjection is more free-form. If Jackson can deserialize the results of the provided query to the requested Class, then it will. As such, the SELECT clause is much less implicitly restricted in this method.
To use both, you must pass in a N1qlQuery object from the SDK. Such queries can be constructed using factory methods of the N1qlQuery class, for example:
//a version of the query that is constructed from positional parameters
N1qlQuery queryWithParameter = N1qlQuery.parameterized("SELECT name FROM `beer-sample` WHERE name LIKE $0", JsonArray.from("%dog%"));
//let Spring Data execute the query, projecting to the String class
List<String> beerNamesContainingDog = template.findByN1QLProjection(queryWithParameter, String.class);
Quick question regarding this issue.
I have an error unable to get the data from database,
Is there something issue with EF Core or my linq query?
var query = _postRepository.Table
.Where(x => x.Approval == true)
.Include(p => p.Industry)
.GroupBy(grp => new { grp.Industry.Id, grp.Industry.Name })
.Select(s => new JobPostStatistics
{
IndustryId = s.Key.Id,
IndustryName = s.Key.Name,
TotalJobPost = s.Count()
});
return query.Take(6).ToList();
InvalidOperationException: Sequence contains more than one element
Seems in EF RC1 GroupBy cause error, here is reported bug:
GroupBy query cause error Sequence contains more than one element
EF Core 2.1 will not only work, but it will also be capable of translating GroupBy to SQL GROUP BY. The expected release date is Q4 2017. Previous versions also support GroupBy but execute it on the client side, which can be a huge problem if you're using it to retrieve aggregates, like SUM, from the database. Imagine retrieving 2 million rows from the server to calculate the sum on the client side, instead of getting it directly from the database server.
In the meantime, you can always write your own SQL query and map it to an entity or anonymous type, using DbSet.FromSql, i.e. invoking FromSql as a member of an entity collection of your context.
Here you have enabled eager loading by using include keyword. You try with disable lazy loading
Server-side GroupBy-support of EF Core has been postponed to after the release: https://github.com/aspnet/EntityFramework/issues/2341
When you log the queries EF creates you can see that it does not create GROUP BY in the SQL.
Here somebody else posted the same error with another GroupBy query.
https://github.com/aspnet/EntityFramework/issues/4775
I had another error with GroupBy and Include(). As EF does not support GroupBy in the SQL and the grouping is done on the client side, I split my query into a server side part and a client side part. The first part queries from the database with the Include() into an anonymous type. Then I do the grouping on the client side.
var event2Country = DbContext.Event2Countries
.Include(j => j.Location)
.Select(j => new { j.Location.Id, j.Location.Name })
.AsNoTracking();
viewModel.MostUsedCountries = event2Country
.GroupBy(j => new { j.Id, j.Name })
.OrderByDescending(j => j.Count())
.ThenBy(j => j.Key.Id)
.Select(j => new SimpleListCountViewModel()
{
Id = j.Key.Id,
Name = j.Key.Name,
Count = j.Count()
})
.Take(15)
.ToList();
Currently you cannot use GroupBy in EF Core if you have a lot of data. A workaround would be to use FromSql. See issue 4959 on Github.
I have read many posts about creating service layer in liferay. I was able to build a service layer and custom query sample project in eclipse. However, all of the examples I got so far is about adding new entities and performing CRUD actions on those new entities.
I want to ask is it possible to use custom query with built-in entities?. For example, I want to use custom query with JounalArticle, AssetEntry, and so on.
If that possible, how can I do that. Please give me some hints or examples.
(I have tried dynamic queries with sub queries but they do not meet my requirements)
If someone is interested:
In the XXXLocalServiceImpl you can add:
public List<JournalArticle> getArticles(String username) {
Session session = xxxPersistence.openSession();
try {
String sql = "SELECT * FROM journalarticle ja WHERE ja.userName like '%"+username+"%'";
SQLQuery query = session.createSQLQuery(sql);
return query.list();
}finally {
session.close();
}
}
rerun your service builder and you can use form XXXLocalServiceUtil.getArticles("Test Test")
Using service builder: create database portlets