I'm learning this wonderful library, however while simple queries work, I'm confused how to write something that not in library FAQ.
For example,
create table if not exists ticks
(id bigserial not null constraint ticks_pkey primary key,
timestamp timestamp not null
);
It it possible to write something like
select coalesce(max(id), 0) from ticks where timestamp::date = ?
Actually, I have 2 issues here
column.max() doesn't have any suitable modifiers, for example, function() accepts no parameters. Probably, I can emulate this in code after I fetch the row.
I have no idea how to make casting in where or write arbitrary where condition.
If it's possible to map object to your existing table then you could try something like:
object Ticks : LongIdTable() {
val timestamp = datetime("timestamp ")
}
fun Expression<DateTime>.pgDate() = object : org.jetbrains.exposed.sql.Function<DateTime>(DateColumnType(false)) {
override fun toQueryBuilder(queryBuilder: QueryBuilder) = queryBuilder {
append(this#pgDate, "::date")
}
}
val expr = Coalesce(Ticks.id.max(), longLiteral(0))
Ticks.slice(expr).select {
Ticks.timestamp.pgDate() eq DateTime.parse("2019-01-01")
}
Related
I'm trying to query dynamoDB through withFilterExpression. I get an error as the argument is a composite key
Filter Expression can only contain non-primary key attributes: Primary key attribute: question_id
and also as it uses OR operator in the query and it cannot be passed to withKeyConditionExpression.
The query that was passed to withFilterExpression is similar to this question_id = 1 OR question_id = 2. The entire code is like follows
def getQuestionItems(conceptCode : String) = {
val qIds = List("1","2","3")
val hash_map : java.util.Map[String, Object] = new java.util.HashMap[String, Object]()
var queries = ArrayBuffer[String]()
hash_map.put(":c_id", conceptCode)
for ((qId, index) <- qIds.zipWithIndex) {
val placeholder = ":qId" + index
hash_map.put(placeholder, qId)
queries += "question_id = " + placeholder
}
val query = queries.mkString(" or ")
val querySpec = new QuerySpec()
.withKeyConditionExpression("concept_id = :c_id")
.withFilterExpression(query)
.withValueMap(hash_map)
questionsTable.query(querySpec)
}
Apart from withFilterExpression and withConditionExpression is there any other methods that I can use which is a part of QuerySpec ?
Let's raise things up a level. With a Query (as opposed to a GetItem or Scan) you provide a single PK value and optionally an SK condition. That's what a Query requires. You can't provide multiple PK values. If you want multiple PK values, you can do multiple Query calls. Or possibly you may consider a Scan across all PK values.
You can also consider having a GSI that presents the data in a format more suitable to efficient lookup.
Side note: With PartiQL you can actually specify multiple PK values, up to a limit. So if you really truly want this, that's a possibility. The downside is it raises things up to a new level of abstraction and can make inefficiencies hard to spot.
I find myself in need of inserting a sequence of elements with a sequence of nested elements into a PostgreSQL database, preferably with a single statement, because I am returning a Future. I am using Scala Play with Anorm.
My data looks something like below.
case class Question(id: Long, titel: String)
case class Answer(questionId: Long, text: String)
In db it looks like this:
CREATE TABLE questions (
question_id SERIAL PRIMARY KEY NOT NULL,
titel TEXT NOT NULL,
);
CREATE TABLE answers (
answer_id SERIAL PRIMARY KEY NOT NULL,
question_id INT NOT NULL,
text TEXT NOT NULL,
FOREIGN KEY (question_id) REFERENCES questions(question_id) ON DELETE CASCADE
);
My function would look something like this:
def saveFormQuestions(questions: Seq[Question], answers: Seq[Answer]): Future[Long] = {
Future {
db.withConnection{ implicit c =>
SQL(
// sql
).executeInsert()
}
}
}
Somehow, in Anorm, SQL or both, I have to do the following, preferably in a single transaction:
foreach question in questions
insert question into questions
foreach answer in answers, where answer.questionId == old question.id
insert answer into answers with new question id gained from question insert
I am new with Scala Play, so I might have made some assumptions I shouldn't have. Any ideas to get me started would be appreciated.
I solved it with logic inside the db.withConnection block. Somehow I assumed that you had to have a single SQL statement inside db.withConnection, which turned out not to be true. So like this:
val idMap = scala.collection.mutable.Map[Long,Long]() // structure to hold map of old ids to new
db.withConnection { implicit conn =>
// save all questions and gather map of the new ids to the old
for (q <- questions) {
val id: Long = SQL("INSERT INTO questions (titel) VALUES ({titel})")
.on('titel -> q.titel)
.executeInsert(scalar[Long].single)
idMap(q.id) = id
}
// save answers with new question ids
if (answers.nonEmpty) {
for (a <- answers ) {
SQL("INSERT INTO answers (question_id, text) VALUES ({qid}, {text});")
.on('qid -> idMap(a.questionId), 'text -> a.text).execute()
}
}
}
As indicated by its name, Anorm is not an ORM, and won't generate the statement for you.
You will have to determine the statements appropriate the represent the data and relationships (e.g. my Acolyte tutorial).
As for transaction, Anorm is a thin/smart wrapper around JDBC, so JDBC transaction semantic is keep. BTW Play provides .withTransaction on its DB resolution utility.
I am trying to build a criteria of comparing the value of a derived property of adding two fields as shown in
Can I do a math operation inside a createCriteria, i.e.
class SumFormula {
Integer column1
Integer column2
Integer sum
static mapping = {
sum formula: 'column1 + column2'
}
}
and the criteria:
SumFormula.createCriteria().list() {
ne("sum", 100)
}
However I could not make it work with MongoDB. The derived property is always null when printed out.
The above cited post did mention that derived properties are SQL expressions, so the questions is that are the derived properties only available with GORM for SQL? Any alternative for GORM for MongoDB?
derived properties are a Hibernate/SQL specific feature and are not supported in GORM for MongoDB. An alternative is to simply do this in code:
class SumFormula {
Integer column1
Integer column2
Integer getSum() { column1 + column2 }
}
We are facing the same problem. Currently, our workaround is to actually store the derived properties in MongoDB and use the beforeUpdate methods to calculate the values.
def beforeUpdate() {
sum = column1 + column2
}
In my current project i am working with the database which has very strange table structure (All Id Fields in most tables are marked as not nullable and primary while there is not auto increment increment enabled for them those Id fields need to be unique as well).
unfortunately there is not way i can modify DB so i find another why to handle my problem.
I have no issues while querying for data but during insert What i want to do is,
To get max Id from table where entity is about to be inserted and increment it by one or even better use SSELECT max(id) pattern during insert.
I was hoping to use Interceptor inside EF to achieve this but is looks too difficult for me now and all i managed to do is to identify if this is insert command or not.
Can someone help me through my way on this problem? how can i achieve this and set ID s during insert either by selecting max ID or using SELECT max(id)
public void TreeCreated(DbCommandTreeInterceptionContext context)
{
if (context.OriginalResult.CommandTreeKind != DbCommandTreeKind.Insert && context.OriginalResult.DataSpace != DataSpace.CSSpace) return;
{
var insertCommand = context.Result as DbInsertCommandTree;
var property = insertCommand?.Target.VariableType.EdmType.MetadataProperties.FirstOrDefault(x => x.Name == "TableName");
if (property == null) return;
var tbaleName = property?.Value as ReadOnlyCollection<EdmMember>;
var variableReference = insertCommand.Target.VariableType.Variable(insertCommand.Target.VariableName);
var tenantProperty = variableReference.Property("ID");
var tenantSetClause = DbExpressionBuilder.SetClause(tenantProperty, DbExpression.FromString("(SELECT MAX(ID) FROM SOMEHOWGETTABLENAME)"));
var filteredSetClauses = insertCommand.SetClauses.Cast<DbSetClause>().Where(sc => ((DbPropertyExpression)sc.Property).Property.Name != "ID");
var finalSetClauses = new ReadOnlyCollection<DbModificationClause>(new List<DbModificationClause>(filteredSetClauses) { tenantSetClause });
var newInsertCommand = new DbInsertCommandTree(
insertCommand.MetadataWorkspace,
insertCommand.DataSpace,
insertCommand.Target,
finalSetClauses,
insertCommand.Returning);
context.Result = newInsertCommand;
}
}
Unfortunately that concept of Interceptor is a little bit new for me and i do not understand it completely.
UPDATE
I manage to dynamically build that expression so that ID field is now included in insert statement, but the problem here is that I can not use SQL query inside it. whenever i try to use this it always results in some wrong SQL query so is there anyway i tweak insert statement so that this SELECT MAX(ID) FROM TABLE_NAME is executed during insert?
Get the next id from the context, and then set the parameter of the insert command accordingly.
void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
var context = interceptionContext.DbContexts.First() as WhateverYourEntityContainerNameIs;
// get the next id from the database using the context
var theNextId = (from foo in context...)
// update the parameter on the command
command.Parameters["YourIdField"].Value = theNextId;
}
Just bear in mind this is not terribly thread safe; if two users update the same table at exactly the same time, they could theoretically get the same id. This is going to be a problem no matter what update method you use if you manage keys in the application instead of the database. But it looks like that decision is out of your hands.
If this is going to be a problem, you might have to do something more drastic like alter the command.CommandText to replace the value in the values clause with a subquery, for example change
insert into ... values (#YourIdField, ...)
to
insert into ... values ((select max(id) from...), ...)
I've got an array like that
Word array (
{
translation = (
{
name = Roma;
lang = it;
},
{
name = Rome;
lang = en;
}
);
type = provenance;
value = RMU;
},
{
translation = (
{
name = "Milano";
lang = it;
},
{
name = "Milan";
lang = en;
}
);
type = destination;
value = MIL;
},)
The idea is to filter it using an NSPredicate and receive and an array of dictionaries based on the lang key, I'd like to get something like this made by filtering for lang == it,
Word array (
{
name = Roma;
lang = it;
type = provenance;
value = RMU;
},
{
name = "Milano";
lang = it;
type = destination;
value = MIL;
})
I can't simplify the data because it comes from a "JSON" service.
I've tried different predicates using SUBQUERY but none of them works, documentation about SUBQUERY is pretty poor, I'm missing something, probably the problem is that I'd like to receive an object that is really different from the source.
Of course I'm able to obtain that structure enumerating, I'm wondering if there is a shorter solution
This answer from Dave DeLong link to SUBQUERY explanation gave a me a lot of hints about SUBQUERY, but I'm not able to find a solution to my problem.
Can someone give me a hints about?
You can't do this with a predicate. (Well, you could, but it would be stupidly complex, difficult to understand and maintain, and in the end it would be easier to write the code yourself)
NSPredicate is for extracting a subset of data from an existing set. It only* does filtering, because a predicate is simply a statement that evaluates to true or false. If you have a collection and filter it with a predicate, then what happens is the collection starts iterating over its elements and asks the predicate: "does this pass your test?" "does this pass your test?" "does this pass your test?"... Every time that the predicate answers "yes this passes my test", the collection adds that object to a new collection. It is that new collection that is returned from the filter method.
THUS:
NSPredicate does not (easily) allow for merging two sets of data (which is what you're asking for). It is possible (because you can do pretty much anything with a FUNCTION() expression), but it makes for inherently unreadable predicates.
SO:
Don't use NSPredicate to merge your dataset. Do it yourself.