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From ntimof...@apache.org
Subject [cayenne-website] branch asf-site updated: Update 4.1 docs
Date Thu, 30 Jul 2020 15:31:24 GMT
This is an automated email from the ASF dual-hosted git repository.

ntimofeev pushed a commit to branch asf-site
in repository https://gitbox.apache.org/repos/asf/cayenne-website.git


The following commit(s) were added to refs/heads/asf-site by this push:
     new d71f0ea  Update 4.1 docs
d71f0ea is described below

commit d71f0ea145ac7bd24890e417cb93628a42f86c9f
Author: Nikita Timofeev <stariy95@gmail.com>
AuthorDate: Thu Jul 30 18:31:04 2020 +0300

    Update 4.1 docs
---
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diff --git a/docs/4.1/cayenne-guide/index.html b/docs/4.1/cayenne-guide/index.html
index 5d7cfc6..3af54fc 100644
--- a/docs/4.1/cayenne-guide/index.html
+++ b/docs/4.1/cayenne-guide/index.html
@@ -1565,7 +1565,7 @@ ORDER BY COUNT(t1.PAINTING_ID) DESC, t0.ARTIST_NAME</code></pre>
     </div> 
    </div> 
    <div class="sect3"> 
-    <h4 id="sqlselect-and-sqlexec"><a class="anchor" href="#sqlselect-and-sqlexec"></a>2.6.3.
SQLSelect and SQLExec</h4> 
+    <h4 id="sqlselect"><a class="anchor" href="#sqlselect"></a>2.6.3. SQLSelect
and SQLExec</h4> 
     <div class="paragraph"> 
      <p>SQL is very powerful and allows to manipulate data in ways that can not always
be described as a graph of related entities. Cayenne acknowledges this fact and provides a
facility to execute SQL, sometimes allowing to map results back to persistent objects. <code>SQLSelect</code>
and <code>SQLExec</code> are a pair of queries that allow to run native SQL. <code>SQLSelect</code>
can be used (as the name suggests) to select custom data in form of entities, separate columns,
collecti [...]
     </div> 
@@ -2500,64 +2500,75 @@ query.prefetch(Artist.PAINTINGS.dot(Painting.GALLERY).disjoint());</code></pre>
     <div class="paragraph"> 
      <p>If a query is fetching DataRows, all "disjoint" prefetches are ignored, only
"joint" prefetches are executed (see prefetching semantics discussion below for what disjoint
and joint prefetches mean).</p> 
     </div> 
-    <div class="sect4"> 
-     <h5 id="prefetching-semantics"><a class="anchor" href="#prefetching-semantics"></a>2.8.1.1.
Prefetching Semantics</h5> 
-     <div class="paragraph"> 
-      <p>Prefetching semantics defines a strategy to prefetch relationships. Depending
on it, Cayenne would generate different types of queries. The end result is the same - query
root objects with related objects fully resolved. However semantics can affect performance,
in some cases significantly. There are 3 types of prefetch semantics, all defined as constants
in <code>org.apache.cayenne.query.PrefetchTreeNode</code>:</p> 
-     </div> 
-     <div class="listingblock"> 
-      <div class="content"> 
-       <pre class="highlight"><code>PrefetchTreeNode.JOINT_PREFETCH_SEMANTICS
+    <div class="paragraph"> 
+     <p>A strategy to prefetch relationships is defined by prefetch "semantics". Depending
on semantics, Cayenne would generate different types of queries. The end result is the same
- query root objects with related objects fully resolved. However semantics can affect performance,
in some cases significantly. There are 3 types of prefetch semantics defined as constants
in <code>org.apache.cayenne.query.PrefetchTreeNode</code>:</p> 
+    </div> 
+    <div class="listingblock"> 
+     <div class="content"> 
+      <pre class="highlight"><code>PrefetchTreeNode.JOINT_PREFETCH_SEMANTICS
 PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS
 PrefetchTreeNode.DISJOINT_BY_ID_PREFETCH_SEMANTICS</code></pre> 
-      </div> 
-     </div> 
-     <div class="paragraph"> 
-      <p>There’s no limitation on mixing different types of semantics in the same
query. Each prefetch can have its own semantics. <code>SelectQuery</code> uses
<code>DISJOINT_PREFETCH_SEMANTICS</code> by default. <code>ObjectSelect</code>
requires explicit semantics as we’ve seen above. <code>SQLTemplate</code> and
<code>ProcedureQuery</code> are both using <code>JOINT_PREFETCH_SEMANTICS</code>
and it can not be changed due to the nature of those two queries.</p> 
      </div> 
     </div> 
-    <div class="sect4"> 
-     <h5 id="disjoint-prefetching-semantics"><a class="anchor" href="#disjoint-prefetching-semantics"></a>2.8.1.2.
Disjoint Prefetching Semantics</h5> 
-     <div class="paragraph"> 
-      <p>This semantics results in Cayenne generatiing one SQL statement for the main
objects, and a separate statement for each prefetch path (hence "disjoint" - related objects
are not fetched with the main query). Each additional SQL statement uses a qualifier of the
main query plus a set of joins traversing the prefetch path between the main and related entity.</p>

-     </div> 
-     <div class="paragraph"> 
-      <p>This strategy has an advantage of efficient JVM memory use, and faster overall
result processing by Cayenne, but it requires (1+N) SQL statements to be executed, where N
is the number of prefetched relationships.</p> 
-     </div> 
+    <div class="paragraph"> 
+     <p><strong>Disjoint prefetch semantics</strong> results in Cayenne
generating one SQL statement for the main objects, and a separate statement for each prefetch
path (hence "disjoint" - related objects are not fetched with the main query). Each additional
SQL statement uses a qualifier of the main query plus a set of joins traversing the prefetch
path between the main and related entity.</p> 
     </div> 
-    <div class="sect4"> 
-     <h5 id="disjoint-by-id-prefetching-semantics"><a class="anchor" href="#disjoint-by-id-prefetching-semantics"></a>2.8.1.3.
Disjoint-by-ID Prefetching Semantics</h5> 
-     <div class="paragraph"> 
-      <p>This is a variation of disjoint prefetch where related objects are matched
against a set of IDs derived from the fetched main objects (or intermediate objects in a multi-step
prefetch). Cayenne limits the size of the generated WHERE clause, as most DBs can’t parse
arbitrary large SQL. So prefetch queries are broken into smaller queries. The size of is controlled
by the DI property <code>Constants.SERVER_MAX_ID_QUALIFIER_SIZE_PROPERTY</code>
(the default number of conditions in t [...]
-     </div> 
-     <div class="paragraph"> 
-      <p>The advantage of this type of prefetch is that matching database rows by ID
may be much faster than matching the qualifier of the original query. Moreover this is <strong>the
only type of prefetch</strong> that can handle SelectQueries with <strong>fetch</strong>
limit. Both joint and regular disjoint prefetches may produce invalid results or generate
inefficient fetch-the-entire table SQL when fetch limit is in effect.</p> 
-     </div> 
-     <div class="paragraph"> 
-      <p>The disadvantage is that query SQL can get unwieldy for large result sets,
as each object will have to have its own condition in the WHERE clause of the generated SQL.</p>

-     </div> 
+    <div class="paragraph"> 
+     <p>This strategy has an advantage of efficient JVM memory use, and faster overall
result processing by Cayenne, but it requires (1+N) SQL statements to be executed, where N
is the number of prefetched relationships.</p> 
     </div> 
-    <div class="sect4"> 
-     <h5 id="joint-prefetching-semantics"><a class="anchor" href="#joint-prefetching-semantics"></a>2.8.1.4.
Joint Prefetching Semantics</h5> 
-     <div class="paragraph"> 
-      <p>Joint semantics results in a single SQL statement for root objects and any
number of jointly prefetched paths. Cayenne processes in memory a cartesian product of the
entities involved, converting it to an object tree. It uses OUTER joins to connect prefetched
entities.</p> 
-     </div> 
-     <div class="paragraph"> 
-      <p>Joint is the most efficient prefetch type of the three as far as generated
SQL goes. There’s always just 1 SQL query generated. Its downsides are the potentially increased
amount of data that needs to get across the network between the application server and the
database, and more data processing that needs to be done on the Cayenne side.</p> 
-     </div> 
+    <div class="paragraph"> 
+     <p><strong>Disjoint-by-ID prefetch semantics</strong> is a variation
of disjoint prefetch where related objects are matched against a set of IDs derived from the
fetched main objects (or intermediate objects in a multi-step prefetch). Cayenne limits the
size of the generated WHERE clause, as most DBs can’t parse arbitrary large SQL. So prefetch
queries are broken into smaller queries. The size of is controlled by the DI property <code>Constants.SERVER_MAX_ID_QUALIFIER_SIZE_PROPERTY<
[...]
     </div> 
-    <div class="sect4"> 
-     <h5 id="similar-behaviours-using-ejbql"><a class="anchor" href="#similar-behaviours-using-ejbql"></a>2.8.1.5.
Similar Behaviours Using EJBQL</h5> 
-     <div class="paragraph"> 
-      <p>It is possible to achieve similar behaviours with <a href="#ejbql">EJBQLQuery</a>
queries by employing the "FETCH" keyword.</p> 
-     </div> 
-     <div class="listingblock"> 
-      <div class="content"> 
-       <pre class="highlight"><code class="language-SQL SQL" data-lang="SQL">SELECT
a FROM Artist a LEFT JOIN FETCH a.paintings</code></pre> 
-      </div> 
+    <div class="paragraph"> 
+     <p>The advantage of this type of prefetch is that matching database rows by ID
may be much faster than matching the qualifier of the original query. Moreover this is <strong>the
only type of prefetch</strong> that can handle SelectQueries with <strong>fetch</strong>
limit. Both joint and regular disjoint prefetches may produce invalid results or generate
inefficient fetch-the-entire table SQL when fetch limit is in effect.</p> 
+    </div> 
+    <div class="paragraph"> 
+     <p>The disadvantage is that query SQL can get unwieldy for large result sets,
as each object will have to have its own condition in the WHERE clause of the generated SQL.</p>

+    </div> 
+    <div class="paragraph"> 
+     <p><strong>Joint prefetch semantics</strong> results in a single SQL
statement for root objects and any number of jointly prefetched paths. Cayenne processes in
memory a cartesian product of the entities involved, converting it to an object tree. It uses
OUTER joins to connect prefetched entities.</p> 
+    </div> 
+    <div class="paragraph"> 
+     <p>Joint is the most efficient prefetch type of the three as far as generated
SQL goes. There’s always just 1 SQL query generated. Its downsides are the potentially increased
amount of data that needs to get across the network between the application server and the
database, and more data processing that needs to be done on the Cayenne side.</p> 
+    </div> 
+    <div class="paragraph"> 
+     <p><code><a href="#select">ObjectSelect</a></code> query
supports all three types of semantics. You can mix and match them in the same query for different
prefetches.</p> 
+    </div> 
+    <div class="paragraph"> 
+     <p><code><a href="#sqlselect">SQLSelect</a></code> query
supports "JOINT" and "DISJOINT_BY_ID". It does not work with "DISJOINT", as the query does
not provide enough information to Cayenne to build dependent prefetch queries. So "DISJOINT"
will result in exception. "JOINT" prefetching requires a bit of effort shaping the SQL to
include the right columns in the result and label them properly to be convertable into object
properties. The main rules to follow are:</p> 
+    </div> 
+    <div class="ulist"> 
+     <ul> 
+      <li> <p>Include <em>all</em> columns from the root entity and
every prefetched entity.</p> </li> 
+      <li> <p>Label each prefetched entity columns as "dbRelationship.column".</p>
</li> 
+     </ul> 
+    </div> 
+    <div class="paragraph"> 
+     <p>E.g.:</p> 
+    </div> 
+    <div class="listingblock"> 
+     <div class="content"> 
+      <pre class="highlight"><code class="language-Java Java" data-lang="Java">List&lt;Artist&gt;
objects = SQLSelect.query(Artist.class, "SELECT "
+    + "#result('ESTIMATED_PRICE' 'BigDecimal' '' 'paintingArray.ESTIMATED_PRICE'), "
+    + "#result('PAINTING_TITLE' 'String' '' 'paintingArray.PAINTING_TITLE'), "
+    + "#result('GALLERY_ID' 'int' '' 'paintingArray.GALLERY_ID'), "
+    + "#result('PAINTING_ID' 'int' '' 'paintingArray.PAINTING_ID'), "
+    + "#result('t1.ARTIST_ID' 'int' '' 'paintingArray.ARTIST_ID'), "
+    + "#result('ARTIST_NAME' 'String'), "
+    + "#result('DATE_OF_BIRTH' 'java.util.Date'), "
+    + "#result('t0.ARTIST_ID' 'int' '' 'ARTIST_ID') "
+    + "FROM ARTIST t0, PAINTING t1 "
+    + "WHERE t0.ARTIST_ID = t1.ARTIST_ID")
+    .addPrefetch(Artist.PAINTING_ARRAY.joint())
+    .select(context);</code></pre> 
      </div> 
-     <div class="paragraph"> 
-      <p>In this case, the Paintings that exist for the Artist will be obtained at
the same time as the Artists are fetched. Refer to third-party query language documentation
for further detail on this mechanism.</p> 
+    </div> 
+    <div class="paragraph"> 
+     <p><code><a href="#ejbql">EJBQLQuery</a></code> uses the
"FETCH" keyword to enable prefetching:</p> 
+    </div> 
+    <div class="listingblock"> 
+     <div class="content"> 
+      <pre class="highlight"><code class="language-SQL SQL" data-lang="SQL">SELECT
a FROM Artist a LEFT JOIN FETCH a.paintings</code></pre> 
      </div> 
     </div> 
    </div> 
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