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<div class="subTitle">org.apache.spark.sql.sources</div>
<h2 title="Class BaseRelation" class="title">Class BaseRelation</h2>
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<li>java.lang.Object</li>
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<li>org.apache.spark.sql.sources.BaseRelation</li>
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<pre>public abstract class <span class="strong">BaseRelation</span>
extends java.lang.Object</pre>
<div class="block">::DeveloperApi::
Represents a collection of tuples with a known schema. Classes that extend BaseRelation must
be able to produce the schema of their data in the form of a <code>StructType</code>. Concrete
implementation should inherit from one of the descendant <code>Scan</code> classes, which define various
abstract methods for execution.
<p>
BaseRelations must also define a equality function that only returns true when the two
instances will return the same data. This equality function is used when determining when
it is safe to substitute cached results for a given relation.
<p></div>
<dl><dt><span class="strong">Since:</span></dt>
<dd>1.3.0</dd></dl>
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<td class="colOne"><code><strong><a href="../../../../../org/apache/spark/sql/sources/BaseRelation.html#BaseRelation()">BaseRelation</a></strong>()</code> </td>
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<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/spark/sql/sources/BaseRelation.html#needConversion()">needConversion</a></strong>()</code>
<div class="block">Whether does it need to convert the objects in Row to internal representation, for example:
java.lang.String -> UTF8String
java.lang.Decimal -> Decimal</div>
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<td class="colFirst"><code>abstract <a href="../../../../../org/apache/spark/sql/types/StructType.html" title="class in org.apache.spark.sql.types">StructType</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/spark/sql/sources/BaseRelation.html#schema()">schema</a></strong>()</code> </td>
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<td class="colFirst"><code>long</code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/spark/sql/sources/BaseRelation.html#sizeInBytes()">sizeInBytes</a></strong>()</code>
<div class="block">Returns an estimated size of this relation in bytes.</div>
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<td class="colFirst"><code>abstract <a href="../../../../../org/apache/spark/sql/SQLContext.html" title="class in org.apache.spark.sql">SQLContext</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/spark/sql/sources/BaseRelation.html#sqlContext()">sqlContext</a></strong>()</code> </td>
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<h4>BaseRelation</h4>
<pre>public BaseRelation()</pre>
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<h4>sqlContext</h4>
<pre>public abstract <a href="../../../../../org/apache/spark/sql/SQLContext.html" title="class in org.apache.spark.sql">SQLContext</a> sqlContext()</pre>
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<h4>schema</h4>
<pre>public abstract <a href="../../../../../org/apache/spark/sql/types/StructType.html" title="class in org.apache.spark.sql.types">StructType</a> schema()</pre>
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<pre>public long sizeInBytes()</pre>
<div class="block">Returns an estimated size of this relation in bytes. This information is used by the planner
to decided when it is safe to broadcast a relation and can be overridden by sources that
know the size ahead of time. By default, the system will assume that tables are too
large to broadcast. This method will be called multiple times during query planning
and thus should not perform expensive operations for each invocation.
<p>
Note that it is always better to overestimate size than underestimate, because underestimation
could lead to execution plans that are suboptimal (i.e. broadcasting a very large table).
<p></div>
<dl><dt><span class="strong">Returns:</span></dt><dd>(undocumented)</dd><dt><span class="strong">Since:</span></dt>
<dd>1.3.0</dd></dl>
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<h4>needConversion</h4>
<pre>public boolean needConversion()</pre>
<div class="block">Whether does it need to convert the objects in Row to internal representation, for example:
java.lang.String -> UTF8String
java.lang.Decimal -> Decimal
<p>
If <code>needConversion</code> is <code>false</code>, buildScan() should return an <code>RDD</code> of <code>InternalRow</code>
<p>
Note: The internal representation is not stable across releases and thus data sources outside
of Spark SQL should leave this as true.
<p></div>
<dl><dt><span class="strong">Returns:</span></dt><dd>(undocumented)</dd><dt><span class="strong">Since:</span></dt>
<dd>1.4.0</dd></dl>
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